Abstract： AIM: To observe the progression of proliferation and apoptosis of colorectal preneoplastic sequence,and to explore the potential role of abnormal expression pattern of PPAR-γ and β-catenin in the preneoplastic sequence.METHODS: Colorectal ACFs and adenomas were induced using a modified DMH-induced carcinogenesis method in SD rats. The expression patterns of PPAR-γ and β-catenin in colorectal preneoplastic sequence were detected using immumohistochemisty. Proliferation and apoptosis of preneoplastic sequence were analyzed using Ki-67 and Bcl-2.RESULTS: In the "Normal-ACF-Adenoma" sequence induced by DMH,abnormal expression of Ki-67 occurred at the transformation stage of "Normal-ACF". Positive nucleuses of Ki-67 distributed extensively within the aberrant crypt,differing from normal crypt significantly and similar to adenoma. Abnormally high expression of Bcl-2 appeared until ACF transformed to adenoma,presenting broad positive granules in the cytoplasm. PPAR-γ,as Ki-67 did,abnormally expressed during the "Normal-ACF" shift with extensive distribution of positive nucleuses. Β-catenin,as Bcl-2 did,presented with different positive location and density until the transformation of "ACF-Adenoma" with evident positive nucleuses.CONCLUSION: In the stage of "Normal-ACF",the main abnormality is higher proliferation rate found in aberrant crypt than normal crypt,and this change might be correlated to abnormal expression of PPAR-γ. Depression of apoptosis became obvious in the stage of "ACF-Adenoma",and the elevated expression of β-catenin and Bcl-2 might have a synergic role in the formation of adenoma.