Abstract: Signal transducer and activator of transcription 3 (STAT3) is an important regulatory factor of cell proliferation and metastasis, involved in the occurrence and development of a variety of malignant tumors, and it is one of the hot spots in the research of targeted anti-tumor drugs. Our group screened a novel benzobis (imidazole) structure small molecule compound LZJ541 through the screening model of Janus kinase (JAK)/STAT3 pathway inhibitors, which has definite STAT3 inhibitory activity. We examined the effect of LZJ541 on the proliferation of HepG2 and PC-3 cells by MTT assay in vitro, detected the effect of LZJ541 on the expression of STAT3-related proteins in HepG2 cells by Western blot, and measured the effect of LZJ541 on the apoptosis and cell cycle arrest of HepG2 cells via flow cytometry. The results indicated that LZJ541 significantly inhibited the activation of STAT3 signaling pathway and restrained the proliferation of HepG2 cells. Its half maximal inhibitory concentration (IC₅₀) was 13.8 μmol·L^-1, which was much lower than that of PC-3 cells (with low STAT3 expression, IC₅₀:41.99 μmol·L^-1), LZJ541 can also inhibit the phosphorylation of STAT3 in HepG2 cells, thereby inducing apoptosis and cycle arrest and then exerting anti-tumor effects. In conclusion, LZJ541 has a certain anti-tumor effect in vitro, which provides an experimental basis for the development of new STAT3-targeted anti-tumor drugs around this kind of compounds.