Objective:To disclose the effect of miR-340-5p on HBV replication and its regulatory mechanism, furthermore provide new strategies for biomarkers and therapeutic drugs after HBV infection.Methods:The miR-340-5p mimic (340-mimic) and inhibitor (340-inhibitor) and their corresponding negative controls were transfected into liver cancer cells HepG2.2.15. The changes of HBeAg and HBsAg levels in the supernatant were detected by ELISA. At the same time, the RNA and the encapsidated DNA were extracted in collected cells, and qRT-PCR was used to detect the levels of HBV total RNA and pgRNA and the changes in HBV DNA copy numbers; qRT-PCR and Western blotting were used to verify the mRNA and protein expression of STAT3; in addition, after co-transformation of miR-340-5p mimic (340-mimic) and pEF-flag-stat3, the replication of HBV was detected by Northern blotting, qPCR and ELISA.Results:When miR-340-5p is overexpressed, the levels of total RNA produced by HBV transcription and the reverse transcription template pgRNA decreased significantly to 45.89% and 61.46% of the control group ( P=0.001, P=0.003); the synthesis of encapsidated DNA and the secretion levels of HBeAg and HBsAg were inhibited by 72.46%, 18.27% and 14.42% respectively ( P<0. 001, P<0. 001, P=0.005), while interference with endogenous miR-340-5p increased 44.02%, 45.56%, 22.66%, 11.85%, and 14.04% respectively compared with the control group ( P=0. 009, P=0. 080, P=0. 011, P=0.013, P=0.027). In contrast, overexpression of signal transducer and activator of transcription (STAT) 3 on this basis can attenuate the inhibition of HBV replication by miR-340-5p. The data also shows that STAT3 promotes HBV replication. Further experimental result also showed that STAT3 could promote the replication of HBV. Conclusions:miR-340-5p can suppress the transcription and translation of STAT3 by targeting it, thereby inhibiting the replication of HBV.