【Abstract】Objective It is to approach the relationships of protein expression of cyclinD1 and Ki67 with development of gastrointestinal stromal tumors by detecting the expression of CyclinD1 and Ki67,and to provide objective indicators of GIST biologic behavior judgment and prognosis. Methods The expression of CyclinD1 and Ki67 in GIST were detected by S-P immunohistochemical method．Results The Ki67 labeling index in the Low-risk group,risk group and high-risk group was（4.6±1.6）%、（19.8±7.5）% and（38.6±8.2）% respectively, showing a significant difference between the three groups( P <0.05) . The Ki67 labeling index was related to the tumor size and mitotic count. The expression of cyclin D1 was significantly higher in GISTs than in normal group( P <0.05) .The positive rate of cyclinD1 protein in the Low-risk group,risk group and high-risk group was 36.8%,57.1% and 80.0% respectively. There was a significant difference in the cyclinD1 protein between the three groups. ( P <0.05) . The positive rate of cyclinD1 protein was related to mitotic count, but not related to the tumor size and tumor necrosis. Conclusion Ki67 and cyclinD1 expression could prompt malignant GIST level,the expression of Ki67 and cyclinD1 are closely related with the biological behavior of GIST and may be considered as potential markers for the biological behavior of GIST.