Abstract: Objective 　To evaluate the effect and mechanism of the inducing differentiation of all t rans retinoic acid in the rat C6 glioma. Methods 　By establishing rat C6 glioma brain tumour model, af ter delivering all t rans retinoic acid via syringe injection into the peritoneal cavity, MRI and flow cytometer were employed to inspect tumour volume and cell cycle respectively. Results 　Tumour volume in the t reatment group was smaller than that in the cont rol group ( P < 0. 05), the ratio of the cells at G₁ phase relatively increased ( P < 0. 05) and S phase relatively decreased ( P < 0. 05) in the t reatment group as compared with that of the cont rol group. Conclusion 　All t rans retinoic acid can induce differentiation and inhibit proliferation on rat C6 glioma, it s mechanism is concerned with the changes of the cell cycle.