The derivatives of acridine play important roles as dyes, drugs, and antiseptics. Herein, we have investigated the kinetics and the mechanism of the formation of 3,8-dimethyl-3H-imidazo[4,5-a]acridine-11-carbonitrile as an imidazo-acridine derivative by using density functional theory. The kinetics and the mechanism of the reaction are investigated without and by considering catalytic effects of the OH−. The proposed mechanisms involve three main steps. Firstly, a tautomerization reaction occurs via an intramolecular proton transfer. Then, the intramolecular cyclization reaction creates a new six-membered ring. The final step is an intramolecular condensation reaction, which results in formation of the acridine product. Barrier energy of the reaction was significantly decreased in the OH− catalyzed pathway. In this proper pathway, the intramolecular cyclization is the rate-determining step of the reaction.