The effects of all-trans retinoic acid (ATRA) on primary gastric carcinoma models made by subcutaneous implanting gastric cancer to mice were observed. Thirty-two cancer bearing nude mice were randomly divided into 4 groups: control group (group Ⅰ)， ATRA low dose feeding group (100μg/day， group Ⅱ), moderate dose feeding group (300μg/day， group Ⅲ), and high dose feeding group (1 000 μg/day, group Ⅳ). The alteration of tumor growth, morphology, cytobiology, and immuno-histochemical assay were perfermed. The results showed significant inhibition of tumor growth and inducing differentiation in the group Ⅲ and group Ⅳ as compared with group Ⅰ (Ｐ＜0.01),and inhibited expression of p53, p21 protein in implanted tumor. The authors consider that ATRA has some effects of growth inhibition and differentiation on gastric cancer cells in vivo, and these is related to the inhibition of expression p53 and p21 onco-gene of cancer cells and accelerate apoptosis of carcinoma cells.