The production of substituted (S)-Aminotetralins requires biocatalyst that have high activities at high temperatures and considerable tolerance to amine donors to shift the reaction towards products. The biocatalyst used in this process are (S)-Aminotransferases. An (S)-aminotransferase of a high activity derived from Athrobacter citreous by directed evolution for the production of substituted (S)-aminotetralin was characterized in the form of whole cells. Its optimum conditions were pH 7 and 55 °C. Maximum activity was 0.21 mM/min per gram of whole cells. Substrate affinities were 750 mM for isopropylamine and 10.4 mM for substituted tetralone. A kinetic study to describe the production of substituted (S)-aminotetralin showed that two major reactions were involved: one enzyme catalyzed –by (S)-aminotransferase- that is the production of substituted (S)-aminotetralin from isopropylamine and substituted tetralone; the other a non-enzyme catalyzed reaction that forms a byproduct consisting in the imine formed by substituted tetralone and substituted (S)-aminotetralin.