Abstract: There were significant differences in morphology, physiology and biochemistry between the original strain 4541 and the mutant strain D-756 of griseofulvin producing strains. In order to understand the genetic background differences between the two strains and make clear their phylogenetic relationships, the ITS and 18S rDNA gene sequences of the mutant strain D-756 and the original strain 4541 were cloned and determined in this study. Then, the homology analysis was conducted and the phylogenetic trees were constructed respectively. The evolutionary tree constructed from the ITS sequence showed that the mutant strain D-756 and the wild strain 4541 were clustered together with the other 3 strains of Penicillium griseofulvum and 1 strain of Penicillium urticae in Genebank. The mutant strain D-756 and the original strain 4541 in the evolutionary tree constructed by 18S rDNA sequence were also clustered with the other 3 strains of Penicillium griseofulvum in Genbank into one branch. The results showed that the original strain 4541 and the mutant strain D-756 belonged to penicillium griseofulvum at the molecular level.