Objective To investigate the expression levels of long non-coding RNA XIST (lncRNA-XIST) in cancer tissues and plasma of gastric cancer patients and its clinical significance. Methods Resected tumor tissues and adjacent non-tumor tissues of 40 patients with gastric cancer in Changhai Hospital of Second Military Medical University were collected from Feb. to Jul. 2017; the plasma samples were collected from 90 patients with gastric cancer and 90 healthy volunteers. The expression level of lncRNA-XIST in the above samples was detected by real-time quantitative PCR (qPCR).The relationship between the expression level of lncRNA-XIST and the clinicopathological parameters related to gastric cancer (age, gender, TNM stage, tumor maximum diameter, lymph node metastasis, differentiation, and Ki-67 positive rate) were analyzed by nonparametric test. The efficacy of plasma lncRNA-XIST in the diagnosis of gastric cancer was evaluated by plotting the receiver operating characteristic (ROC) curve. Results The expression of lncRNA-XIST in tumor tissues was significantly increased compared with adjacent non-tumor tissues (0.150[0.094, 0.247] vs 0.085[0.041, 0.193], P<0.05), and the lncRNA-XIST expression in plasma in the gastric cancer group was significantly higher than that in the healthy group (0.189[0.119, 0.256] vs 0.144[0.095, 0.180], P<0.05). The expression levels of lncRNA-XIST in plasma and cancer tissues of gastric cancer patients were related to TNM staging, lymph node metastasis and differentiation (cancer tissues:Z=3.147, 2.729 and 2.393; plasma:Z=2.769, 2.431 and 2.144; all P<0.05). Area under ROC curve (AUC) performed by plasmatic lncRNA-XIST for gastric cancer was 0.753 (95%CI 0.681-0.825, P<0.001); when the cut-off value was 0.197, the sensitivity was 51.1% and the specificity was 95.6%. The AUC of diagnosing gastric cancer in TNM Ⅰ-Ⅱ was 0.694(95%CI 0.592-0.796, P<0.01), with a sensitivity of 38.5% a the specificity of 95.6%. All values in above two cases were higher than those of carcino-embryonic antigen (CEA), carbohydrate antigen (CA)19-9, CA72-4 alone or combined detection. Conclusion The expression levels of lncRNA-XIST are increased in cancer tissues and plasma of gastric cancer patients, which may be a potential tumor marker for diagnosing gastric cancer.