Aspergillus flavus and Aspergillus oryzae, two species of Aspergillus section Flavi, are of utmost significance in health, medicine, biotechnology, and foods industries. The methods currently used in mycology for the discrimination of these two closely related species were unable to definitively and rapidly distinguish. The present study aimed to develop a restriction fragment length polymorphism (RFLP) test based on the cyp51A gene to discriminate between A. flavus and A. oryzae. The cyp51A gene sequences of A. flavus and A. oryzae reference strains were amplified using the specific primers CYP51AF and CYP51AR. The polymerase chain reaction (PCR) products were subjected to digestion with a restriction enzyme, HincII. The polymerase chain reaction (PCR)- RFLP test created specific patterns for standard strains, as well as clinical and environmental A. flavus and A. oryzae isolates. The one-enzyme PCR-RFLP test on the cyp51A gene designed in the present study is a remarkably simple, reliable, and low-cost method for the accurate and rapid differentiation of A. flavus and A. oryzae isolated from clinical and environmental samples.