Sixty nine specimens of rectal carcinoma were classified by the author conforming to malignancy and infiltration and the relationship between them and 3 and 5 years survivor rate was studied. 1) For malignancy, it was classified into 3 grades conforming to six terms, that is infiltration figure, presence of gland cavity, unequal size of cells, quantity of chromatin and amount of mitosis. The malignancy in each term was generally in parallel. 2) For infiltration without regard to the exsistence of metastasis they were classified into 3 grades; cancer infiltration on the basis of rectal cancer which does not reach to muscle layer, which reaches into muscle layer and which goes beyond muscle layer to the outside of it. 3) According to the late results of the authors' department, the 2 years' survivor rate is 65% and 5 years' is 55%. 4) Relationship between malignancy and 3 years' survivor rate is in the I grade 100%, in the II grade 67% and in the III grade 33%. That between malignancy and 5 years, survivor rate is respectively 60%, 63% and 0%. Drawing a line on the muscle layer, the prognosis shows a big difference between that which does not reach to the line and that which spreads beyond the line. 5) The histological examination before the radical operation of rectal cancer preserving the function of anal sphincter is useful to decide the resection limit of the colon which lays near to the anal side from the lower end of tumor.