The present study aimed to investigate the direct as well as indirect effect (through identity processing styles) of cognitive reasoning processes (rational-experiential processing systems) on identity achievement. In this model, identity processing styles serve as a catalyst for cognitive reasoning and identity achievement. For this purpose, a sample of 250 boys and 250 girls with age ranging from 15-20 years (M = 17.62; SD = 1.85) was taken. Identity Style Inventory-3 (Berzonsky, 1992), Rational Experiential Inventory_x0002_Adolescents (Marks et al., 2008), and Extended Objective Measure of Ego Identity (Bennion & Adams, 1986) were administered on the sample. The mediating role of identity processing styles in the relationship of cognitive reasoning and identity achievement was investigated. The results of Multiple Hierarchical Regression analyses revealed that the relation between rational processing system and identity achievement was partially mediated by informational identity processing style. In addition, the relationship between experiential processing system and identity achievement was completely mediated by two identity processing styles_x0002_informational and normative. The current study findings were considered in terms of socio-cognitive model of formation of identity.