The population structure of Magnaporthe grisea, the causal agent of the rice blast, was analyzed in Mazandaran province, using DNA fingerprinting based on RAPD-PCR by means of three primers including "I", "D" and "H". Total DNA of 47 isolates was extracted and amplified according to a specific PCR program. As a result, variable length fragments were generated. Each isolate was subjected to DNA fingerprinting and clonal lineages were determined. Phenetic analysis differentiated three distinct fingerprint lineages. In order to study on fertility status and distribution of the mating type idiomorphs (alleles), 72 monoconidial isolates from Mazandaran province were paired with four standard fertile hermaphrodite isolates. The mating type of 36 isolates was determined as Mat 1-1. The others (36 isolates) did not form any perithecia in pairing with standard isolates