Objective To investigate the expression of microRNA-340 (miR-340) in hepatocellular carcinoma (HCC) and its effect on cell biological behavior. Methods We collected 40 frozen HCC tissues and adjacent non-tumor tissues from patients undergoing hepatectomy of HCC at The First Affiliated Hospital of Chongqing Medical University from Mar. 2015 to Sep. 2016. The expression of miR-340 in all tissues was detected by qPCR and the relationship between miR-340 expression and clinicopathological parameters was analyzed. Simultaneously, the expression of miR-340 in normal hepatocyte (HL-7702) and four hepatoma cells lines (Hep3B, Bel-7402, HepG2, SMMC-7721) was detected by qPCR after incubation for 48 h. The eukaryotic expression vector with miR-340 or control reagent was transfected into SMMC-7721 cells using EndoFection^TM-Max to increase or inhibit the expression of miR-340, and then the cells were cultured for 24 h, 48 h and 72 h. The proliferation of SMMC-7721 cells was detected by CCK-8 assay, and the apoptosis was detected by flow cytometry. The target gene of miR-340 was predicted by bioinformatics software, and the effect of miR-340 on target gene was further verified by qPCR and Western blotting. Results The expression of miR-340 in HCC tissues was significantly lower than that in the adjacent non-tumor tissues (P<0.01), and was correlated with hepatitis B surface antigen, HBV DNA, tumor size and TNM stage (all P<0.01). Besides, the expression of miR-340 in HL-7702 cells was significantly higher than that in Hep3B, Bel-7402, HepG2 and SMMC-7721 cells (P<0.05, P<0.01). CCK-8 assay results showed that overexpression of miR-340 inhibited proliferation of SMMC-7721 cells, while inhibition of miR-340 promoted cell proliferation (P<0.05, P<0.01). Overexpression of miR-340 significantly promoted SMMC-7721 cells apoptosis, while suppression of miR-340 significantly inhibited cells apoptosis (all P<0.01). S-phase kinase-associated protein 2 (SKP2) was a target gene of miR-340 as indicated by bioinformatics software. Further, qPCR and Western blotting results showed that overexpression of miR-340 inhibited the mRNA and protein expression of SKP2, while inhibition of miR-340 increased the mRNA and protein expression of SKP2. Conclusion The abnormal expression of miR-340 may be associated with the HBV infection, and miR-340 may be an indicator to evaluate the progression and prognosis of HCC. MiR-340 can inhibit proliferation and promote apoptosis of SMMC-7721 cells, which may be effected by inhibiting the SKP2 expression.