Abstract: Objective　To detect the mutations of phosphatidylinositol 3kinase catalytic alpha polypeptide (PIK3CA) gene in colon carcinoma, and analyze the relation and significance with computerized tomography (CT) stages.   Methods　The tumor tissues (78 cases) and tumoradjacent tissues (30 cases) of colon carcinoma were collected. The exon 12 and exon 20 of PIK3CA gene was amplified by polymerase chain reaction (PCR) and examined by singlestrand conformation polymorphism (SSCP) and sequenced. With the CT stages, the data of Dukes stage were analyzed.  Results　In tumor tissues, after the SSCP examination and sequencing, there was no mutation happened in the exon 20, and there were 16(20.51%) cases of the exon 12, which all changed with G1876A mutation in Dukes A stage and B stage. In contrast， all the tumoradjacent tissue cases were not found mutation in exon 12 and exon 20.  Conclusions　The mutation G1876A of PIK3CA gene plays an important role in the genesis of colon carcinoma, and it is useful to analyze and diagnose early colon carcinoma by the detection of exon 12. 

Key words: Phosphatidylinositol 3-kinase catalytic alpha polypeptide gene, Gene mutation, Gene analysis, Singlestrand conformation polymorphism, Sequence