OBJECTIVE To study the effect of epipolythiodioxopiperazine compound C87 on tumor cell proliferation and explore the potential mechanisms. METHODS Tumor cells were exposed to C87 0.05-1 μmol.L-1 for 24, 48 and 72 h, cell viability was determined by sulforhodamine B (SRB) assay and the half growth inhibition (Gl50 ) was calculated. After treatment with C87 0.1-2.5 μmol.L-1 for 6 h, or C87 2.5 μmol.L-1 for 0-6 h, the generation of reactive oxygen species (ROS) was measured using the compound 2′,7′-dichlorofluoresceindiacetate and flow cytometry analysis. After treatment with C87 2.5 μmol.L-1 , either alone or with antioxidant N-acetylcysteine (NAC), for 6 h, the generation of ROS was measured by flow cytometry analysis. Tumor cells were exposed to C87 0.05-1 μmol.L-1 , either alone or with NAC, for 24 and 48 h, while cell viability was determined by SRB assay. RESULTS The cell viability was significantly reduced following exposure to C87 0.05-1 μmol.L-1 for 24, 48 and 72 h in a concentration-dependent manner in A549, HCT116, HeLa and SMMC7721 cells(P<0.05). At 72 h, the value of r2 was 0.946, 0.989, 0.973 and 0.984(P<0.05), respectively. The cell viability was significantly reduced following exposure to C87 1 μmol.L-1 for 24 - 72 h in a time-dependent manner in A549, HCT116, HeLa and SMMC7721 cells(P<0.05). The value of r2 was 0.983, 0.956, 0.951 and 0.873(P<0.05), respectively. The generation of ROS was increased after exposure to C87 0.25-2.5 μmol.L-1 in a concentration-dependent manner in HCT116 and HeLa cells for 6 h (r2 = 0.760, P = 0.045: r2 = 0.987, P=0.001), and after exposure to C87 2.5 μmol.L-1 in a time-dependent manner in HCT116 and HeLa cells for 0.5-6 h (r2 = 0.886, P = 0.017: r2 = 0.994, P = 0.000).The C87-induced ROS generation could be blocked by NAC in HCT116 and HeLa cells(P<0.05). The C87 induced cell death could be blocked by NAC 5 and 10 mmol.L-1 , and the Gl50 value was 1.446 and 1.134 μmol.L-1 for 24 h (the Gl50 value of C87 group was 0.513 μmol.L-1 ), and 0.882 and 1.166 μmol.L-1 for 48 h (the Gl50 value of C87 group was 0.333 μmol.L-1 ). CONCLUSION The novel epipolythiodioxopiperazine derivative C87 exerts potent antitumor activity in vitro, possibly via triggering ROS production.