To establish a method for determination of cantharidin content in Mylabris phalerata. Pallas, and to study its inhibitory and apoptosis-inducing effects on human hepatoma cell line HepG2. Agilent column (TC-C18, 250 mm × 4.6 mm, 5 μm); mobile phase: methanol-water (volume ratio: 20:80); flow rate: 1.0 ml/min; UV detection wavelength: 230 nm; and column temperature: 30°C. MTT assay was used to determine cell viability, and flow cytometry was used to detect the effects of cantharidin on cell cycle arrest and apoptosis of HepG2 cells. Cantharidin had a good linearity (R=0.9993) within a 0.056~0.504 μg range, and had an average recovery of 98.55%. Different concentrations of cantharidin all markedly induced the apoptosis of human hepatoma HepG2 cells. After treatment for 24, 36 and 48 h, respectively, HepG2 cells were inhibited to varying degrees in a dose and time dependent manner. PI staining with flow cytometry showed that the test concentrations of cantharidin could induce HepG2 cell apoptosis, and impact the cell cycle to varying degrees by increasing the proportion of G0/G1 phase cells. Compared with the control group, apoptosis was positively correlated with drug concentration, presenting a marked dose-dependence. The method proposed is simple, fast, accurate and reproducible, which can be used for the determination of cantharidin content in Mylabris phalerata. Pallas. Cantharidin has an inhibitory effect on HepG2 cells.