Usnic acid (UA), a natural botanical product, is a constituent of some dietary supplements used for weight loss. It has been associated with clinical hepatotoxicity leading to liver failure in humans. The present study was undertaken for metabolism and toxicity evaluations of (+)UA on HepG2 cell line in culture.The cells were treated with the vehicle control and (+)UA at concentrations of 0–100 µM for 24 h at 37°C in 5% CO2 incubator. Following the treatment period, the cells were evaluated by biochemical and toxicogenomic endpoints of toxicity that included MTT activity, LDH release. (+)UA exposure resulted in increased cytotoxicity and mitochondrial dysfunction in HepG2 cells. compared with the controls, low non-toxic concentrations of UA separately showed no effect on the cells as determined by the biochemical endpoints compared with higher concentrations (P<0.001).