Analysis of mating type can provide an evaluation of the population genetic diversity of the rice blast fungus, Magnaporthe grisea. According to the sequences of MAT1-1 and MAT1-2 genes of the fungus, two pairs of PCR primers specific to the MAT1-1 and MAT1-2 alleles were designed, and the PCR thermal profile was also optimized. To confirm its application in mating type assessment, 10 tester isolates were tested by PCR. The PCR amplification pattern of these tester isolates corresponded to their known mating type. Furthermore, 150 rice-field isolates from Fujian Province were mated with tester isolates GUY11 and KA3 side by side and also tested by PCR. Results showed that 95.1% of 123 fertile isolates were the same in mating type as determined by both PCR-amplified allele-specific fragments and mating with GUY11/KA3. Among 27 sterile isolates determined by GUY11 and KA3, seven were MAT1-1 and 20 were MAT1-2 as determined by PCR. This study indicates that PCR is applicable in assessing M. grisea mating type and especially is capable of predicting the potential mating type of sterile isolates in the natural population of the fungus.