Objective To explore the expression levels of cytokines in serum of treatment-naive chronic hepatitis B (CHB) patients and its relationships with viral load and liver inflammation, so as to provide new ideas for dynamic assessment of disease and prognosis of CHB.Methods A total of 68 treatment-naive patients with chronic hepatitis B virus (HBV) infection, who were admitted to Department of Infectious Diseases of The First Hospital Affiliated to Naval Medical University (Second Military Medical University) from Oct. 2018 to Nov. 2019, and 12 healthy controls were enrolled. The expression levels of cytokines interleukin (IL)-17A, IL-2, IL-21, and IL-4 in serum were tested by enzyme-linked immunosorbent assay (ELISA). Chemiluminescence method was used to detect HBV serological markers, quantitative polymerase chain reaction (qPCR) was used to detect serum HBV DNA quantification, and automatic biochemical analyzer was used to detect liver function indexes. Spearman correlation analysis was used to evaluate the correlations of serum cytokines with viral load and degree of liver inflammation. Receiver operating characteristic (ROC) curves were drawn to evaluate the efficacy of serum cytokines in judging liver inflammation. Results Compared with the healthy controls, the serum IL-17A and IL-21 levels in the treatment-naive CHB patients were significantly higher (17.50 ［11.99, 25.36］ pg/mL vs 13.74 ［9.07, 16.94］ pg/mL, Z=-2.001, P=0.045; 37.12 (23.85, 77.66) pg/mL vs 20.30［17.9, 24.19］ pg/mL, Z=-3.485, P＜0.01), the IL-2 level was significantly lower (57.19 ［31.10, 79.92］ pg/mL vs 73.06 ［62.41, 105.84］ pg/mL, Z=-2.509, P=0.012), and there was no significant difference in IL-4 level (11.40 ［5.79, 18.62］ pg/mL vs 10.84 ［8.05, 25.20］ pg/mL;Z=-0.681, P=0.496). The expression levels of IL-17A in CHB patients with different disease courses were significantly different (H=8.870, P=0.031). Compared to the patients with inflammatory inactive CHB, the serum IL-17A and IL-21 levels were significantly higher (17.71 ［12.25, 27.92］ pg/mL vs 16.51 ［6.29, 20.22］ pg/mL and 39.29 ［24.71, 83.19］ pg/mL vs 25.06 ［19.37, 49.43］ pg/mL), the IL-2 level was significantly lower (57.19 ［31.10, 77.68］ pg/mL vs 71.24 ［48.07, 117.39］ pg/mL) (allP＜0.05), and there was no significant difference in IL-4 level (11.40 ［5.94, 18.12］ pg/mL vs 14.57 ［3.12, 24.49］ pg/mL,P＞0.05) in the patients with inflammatory active CHB. The levels of serum IL-17A (15.34 ［10.65, 25.04］, 19.98 ［15.55, 34.14］ pg/mL vs 13.74 ［9.07, 16.94］ pg/mL, H=10.061, P=0.007) and IL-21 (37.74 ［25.06, 82.87］, 51.74 ［23.32, 83.82］ pg/mL vs 20.30 ［17.90, 24.19］ pg/mL, H=12.444, P=0.002) in hepatitis B e antigen (HBeAg)-positive CHB patients and HBeAg-negative CHB patients were significantly higher than those in healthy controls, while the level of IL-2 (57.19 ［37.45, 79.92］, 37.45 ［18.32, 73.06］ pg/mL vs 73.06 ［62.41, 105.84］ pg/mL, H=6.576, P=0.037) was significantly lower than that in healthy controls. There were no correlations between serum IL-17A, IL-21, IL-4 levels and HBV DNA quantification in treatment-naive CHB patients (r=0.02, 0.23, 0.07, all P＞0.05), while the level of IL-2 was weakly correlated with HBV DNA quantification (r=0.32, P=0.01). There were correlations between serum IL-17A, IL-21 and alanine transaminase (ALT) (r=0.59, 0.49, both P＜0.01), aspartate transaminase (AST) (r=0.47, 0.36, both P＜0.01) in treatment-naive CHB patients, while IL-2 and IL-4 had no significant correlations with ALT or AST (all P＞0.05). There were statistically significant differences in serum levels of IL-17A, IL-2, and IL-21 among the treatment-naive CHB group with ALT≥300 U/L, the treatment-naive CHB group with ALT＜300 U/L, and healthy control group (all P＜0.05). Specifically, the levels of IL-17A and IL-21 in the treatment-naive CHB group with ALT≥300 U/L were significantly higher than those in the treatment-naive CHB group with ALT＜300 U/L and healthy control group (all P＜0.01). The level of IL-2 in the treatment-naive CHB group with ALT＜300 U/L was significantly lower than that in healthy control group, while the level of IL-21 was significantly higher than that in healthy control group (all P＜0.01). ROC curve analysis results showed that the area under curve (AUC) values of IL-17A and IL-21 to judge the degree of liver inflammation were 0.893 3 (95% confidence interval ［CI］ 0.793 0-0.993 6) and 0.760 0 (95% CI 0.622 7-0.897 3), respectively. Conclusion IL-17A, IL-2, and IL-21 are involved in the progression of chronic HBV infection. Regardless of whether HBeAg is positive or not or the degree of inflammation, the serum levels of IL-17A and IL-21 in the treatment-naive CHB patients are increased, while the level of IL-2 is decreased. IL-2 has a certain correlation with HBV DNA quantification. IL-17A and IL-21 are positively correlated with ALT and AST. Detection of IL-17A and IL-2 is helpful for disease assessment and prognosis.