Abstract: The author computes compounds of series of 4-aminobiphenyl with PM3 method of MOPAC program on SGI workstation. The mechanism of carcinogenic activity of compounds has been gained by applying the mechanism conception of the specialized di-functional alkylation between the nitrenium ion of amino group and expoxide of the aromatic ring. On seeing that the mechanism gained is in accordance with the experimental basis, we should say a good QSAR (quantitative structure carcinogenic activity relationship) is established.