ABSTRACT Aspartic proteases exhibit optimum enzyme activity under acidic condition and have been extensively used in food, fermentation and leather industries. In this study, a novel aspartic protease precursor (pro Tl APA1) from Talaromyces leycettanus was identified and successfully expressed in Pichia pastoris . Subsequently, the auto-activation processing of the zymogen pro Tl APA1 was studied by SDS-PAGE and N-terminal sequencing, under different processing conditions. Tl APA1 shared the highest identity of 70.3 % with the aspartic endopeptidase from Byssochlamys spectabilis (GAD91729) and was classified into a new subgroup of the aspartic protease A1 family, based on evolutionary analysis. Mature Tl APA1 protein displayed an optimal activity at 60 °C and remained stable at temperatures of 55 °C and below, indicating the thermostable nature of Tl APA1 aspartic protease. During the auto-activation processing of pro Tl APA1, a 45 kDa intermediate was identified that divided the processing mechanism into two steps: formation of intermediates, and activation of the mature protein ( Tl APA1). The former step was completely induced by pH of the buffer, while the latter process depended on protease activity. The discovery of the novel aspartic protease Tl APA1 and study of its activation process will contribute to a better understanding of the mechanism of aspartic proteases auto-activation. IMPORTANCE The novel aspartic protease Tl APA1 was identified from T. leycettanus and expressed as a zymogen (pro Tl APA1) in P. pastoris . Enzymatic characteristics of the mature protein were studied and the specific pattern of zymogen conversion was described. The auto-activation processing of pro Tl APA1 proceeded in two stages and an intermediate was identified in this process. These results describe a new subgroup of aspartic protease A1 family and provide insights into a novel mode of activation processing in aspartic proteases.