A recent report showed that the unfolded protein response (UPR) signaling was activated in the pathogenesis of carbon tetrachloride (CCl₄)-induced hepatic fibrosis. Phenylbutyric acid (PBA) is a well-known chemical chaperone that inhibits endoplasmic reticulum (ER) stress and unfolded protein response (UPR) signaling. In the present study, we investigated the effects of PBA on CCl₄-induced hepatic fibrosis in mice. All mice were intraperitoneally (i.p.) injected with CCl₄ (0.15ml/kg BW, twice per week) for 8weeks. In CCl₄+PBA group, mice were i.p. injected with PBA (150mg/kg, twice per day) from the beginning of CCl₄ injection to the end. As expected, PBA significantly attenuated CCl₄-induced hepatic ER stress and UPR activation. Although PBA alleviated, only to a less extent, hepatic necrosis, it obviously inhibited CCl₄-induced tumor necrosis factor alpha (TNF-α) and transforming growth factor beta (TGF-β). Moreover, PBA inhibited CCl₄-induced hepatic nuclear factor kappa B (NF-κB) p65 translocation and extracellular signal-regulated kinase (ERK) and c-Jun N-terminal Kinase (JNK) phosphorylation. Interestingly, CCl₄-induced α-smooth muscle actin (α-SMA), a marker for the initiation phase of HSC activation, was significantly attenuated in mice pretreated with PBA. Correspondingly, CCl₄-induced hepatic collagen (Col)1α1 and Col1α2, markers for the perpetuation phase of HSC activation, were inhibited in PBA-treated mice. Importantly, CCl₄-induced hepatic fibrosis, as determined using Sirius red staining, was obviously attenuated by PBA. In conclusion, PBA prevents CCl₄-induced hepatic fibrosis through inhibiting hepatic inflammatory response and HSC activation.