Objective: To investigate the effect of AG490, an inhibitor of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal transduction pathway, on the growth and apoptosis of hepatocellular carcinoma SMMC-7721 cells in vivo, and to explore the possible mechanism. Methods: The xenograft tumor models of human hepatocellular carcinoma SMMC-7721 cells in nude mice were established. When the subcutaneous transplanted tumor grew to about 150 mm3, the mice were randomly divided into four groups, including saline treated control group, AG490 treated group, cisplatin (DDP) treated group, and AG490 combined with DDP treated group. Then the growth curves of xenograft tumors in different groups were drawn, the inhibitory rates of tumor growth were calculated, and the cell cycle and apoptosis were detected by FCM. The expression levels of phospho-STAT3 (p-STAT3) and caspase-3 in xenograft tumors were detected by immunohistochemistry and Western blotting. Results: Compared with the control group, the size of transplanted tumor was significantly decreased in DDP group, AG490 group and DDP combined with AG490 group after intraperitoneal injection with drugs for 10 and 13 days (all P<0.05). The inhibitory rate of tumor growth in AG490 combined with DDP group (60.24%) was significantly higher than that in DDP group (51.73%) or AG490 group (34.58%) (both P<0.05). The apoptotic rates of DDP group [(22.4±0.8)%], AG490 group [(40.1±1.2)%] and AG490 combined with DDP group [(43.2± 1.5)%] were significantly higher than that in the control group [(11.5±0.4)%] (all P<0.05). The positive rates of p-STAT3 expression in the control group, AG490 group, DDP group and AG490 combined with DDP group were (95.4±1.8)%, (65.8±2.4)%, (37.4±2.1)% and (20.3± 1.2)%, respectively; while the positive rates of caspase-3 expression in the above groups were (10.7±1.1)%, (26.4±1.6)%, (53.9±3.2)% and (82.5±2.8)%, respectively. The expression level of caspase-3 was significantly increased, while the expression level of p-STAT3 was decreased after treatment with AG490, DDP or their combination (all P<0.05). Conclusion: AG490 combined with DDP can further improve the synergistic inhibitory effect of DDP on tumor growth through blocking the expression of p-STAT3 protein and upregulating the expression of apoptosis-related protein caspase-3 in JAK2/STAT3 pathway.