Objective To observe the expression of serine/threonine kinase 31 (STK31) in osteosarcoma and its effect on the malignant biological behavior of osteosarcoma.Methods Fifteen cases of osteosarcoma specimens and adjacent normal tissue were collected.The expression of STK31 in tumor tissues and normal tissue were detected by immunohistochemistry,real-time quantitative PCR and Western blot.The STK31 knockout plasmids PGenesil-STK31-shRNA or control plasmid pGenesil-1 were transfected into osteosarcoma cell line MG63 cells.The effect of STK31 on the proliferation of MG63 cells was detected by CCK8 cell activity assay.Tanswell experiment was used to observed the effect of STK31 on the migration ability of osteosarcoma cells.Results Immunohistochemical showed that STK31 expressed in the tumor tissue,and it was significantly higher than the adjacent normal tissues;Real time quantitative PCR[(3.65±0.83)vs.(1.05±0.14),P＜0.05] and Western blot also revealed that STK31 expression in tumor tissue were significantly higher than adjacent normal tissues(P＜0.05);CCK8 experiments showed that knockdown STK31 inhibited proliferation of MG63 cell when compared with the control group after 36 h[(1.71±0.17)vs.(1.39±0.11),P＜0.05],72 h[(2.15±0.21)vs.(1.54±0.14),P＜0.05];Tansewell experiments showed that transfection of pGenesil-STK31-shRNA could suppress MG63 cell's migration[(13±4)vs.(55±8),P＜0.05].Conclusion STK31 is overexpression in osteosarcoma with increased biological activity of osteosarcoma cells.