Background Hepatitis B is at particularly high risk of fibrosis progression. Unfortunately, the mechanism of hepatic fibrogenesis induced by hepatitis B virus (HBV) has not been fully understood to date. The aim of this study was to observe whether HBV can infect hepatic stellate cells (HSCs), and to examine the effects of HBV or HBV S protein (HBs) on the proliferation and collagen type I expression of HSCs. Methods The supernatants of HepG2.2.15 cells which contained HBV-DNA or HBs were added to LX-2 cells for 72 hours. Cell survival was determined by MTT assay. HBV particles in LX-2 cells were detected by transmission electron microscopy. The expression of HBs and HBV C protein (HBc) was determined by confocal fluorescence microscopy. The expression levels of HBV-DNA were measured by real-time PCR. The cellular collagen type I mRNA and protein levels were quantified by reverse transcription-PCR and ELISA, respectively. Results High concentrations of HBV (1.2x10(5)-5.0x10(5) copies/ml) or HBs (1.25-20 mu g/ml) inhibited the proliferation of LX-2 cells, while low concentrations of HBV (1.0x10(3)-6.2x10(4) copies/ml) or HBs (0.04-0.62 mu g/ml) promoted the proliferation. After treating LX-2 cells with HBV for 72 hours, about 42 nm HBV-sized particles and strong expression of HBs and HBc were found in the cytoplasm of LX-2 cells. HBV-DNA in the culture medium of LX-2 cells decreased at 24 hours, rose at 48 hours and thereafter, decreased again at 72 hours. The mRNA and protein expression of cellular collagen type I in LX-2 cells were significantly increased by HBV infection but not by recombinant HBs. Conclusions HBV and HBs affect the proliferation of HSCs; HBV can transiently infect and replicate in cultured HSCs and express HBs and HBc in vitro. Furthermore, HBV can significantly increase the expression of collagen type I mRNA and protein in HSCs. Chin Med J 2009;122(12):1455-1461