UHF/AM1 method has been applied to study the thermolyses of o-aminobenzoyl, o-amino-p-methylbenzoyl, o-amino-p-formalbenzoyl azides. The results obtained show that these reactions proced through various competing routes yielding to different products, and the activation energy of the rate-determining steps of routes (2)—(4) are lower than that of route(1).