Liver fibrosis, the main characteristic of chronic liver diseases, is strongly associated with the activation of hepatic stellate cells (HSCs), which are responsible for extracellular matrix production. As such, investigating the effective regulators controlling HSC activation provides important clues for developing therapeutics to inhibit liver fibrosis. Thymosin beta 4 (T4), a major actin-sequestering protein, is known to be involved in various cellular responses. A growing body of evidence suggests that T4 has a potential role in the pathogenesis of liver fibrosis and that it is especially associated with the activation of HSCs. However, it remains unclear whether T4 promotes or suppresses the activation of HSCs. Herein, we review the potential role of T4 in liver fibrosis by describing the effects of exogenous and endogenous T4, and we discuss the possible signaling pathway regulated by T4. Exogenous T4 reduces liver fibrosis by inhibiting the proliferation and migration of HSCs. T4 is expressed endogenously in the activated HSCs, but this endogenous T4 displays opposite effects in HSC activation, either as an activator or an inhibitor. Although the role of T4 has not been established, it is apparent that T4 influences HSC activation, suggesting that T4 is a potential therapeutic target for treating liver diseases.