Isocryptotanshinone treatment down-regulated the expression of cell cycle and apoptosis-related proteins cyclin D1, phosphorylated Rb, E2F transcription factor 1 (E2F1), myeloid cell leukemia 1 (Mcl-1), Bcl-2, and survivin expression; inhibited the phosphorylation of STAT3; and induced cell cycle arrest at G1/G0 phase, thereby inhibiting the proliferation of gastric cancer cells. This evidence concerns the gene E2F1 and gastric cancer.