Molecular methods have been established to make better sensitivity and specificity for differentiation of pathogenic and allergenic fungi. The purpose of this study was to obtain an appropriate molecular pattern for differentiation of Penicillium species understudy. In this study, 30 isolates of four Penicillium species including Penicillium citrinum,Penicillium notatum, Penicillium oxalicum and Penicillium frequentans were used. First, isolates were cultured. Then, for obtaining the fungal mats, fungi were grown into Sabouraud glucose broth. Freeze and Thaw, and glass beads were used for cell disruption, and DNA was extracted by phenol-chloroform method. RAPD-PCR technique was performed using three primers. The results showed that each primer produced a different reproduction pattern. A total of 2 to 17 bands were observed in all the isolates ofPenicillium, except P. citrinum C2 and P. frequentans F7. According to primer 1, molecular patterns of Penicillium species were approximately similar, but multiplied patterns were not completely similar. Having used primer 2, multiplied patterns in P. oxalicum and P. notatum were to some extent similar, but there were some observed differences between P. frequentans and two other species P. oxalicum and P. notatum.P. citrinum, P. oxalicum and P. notatum had approximately the same patterns using primer 3, but some differences were observed in P. frequentans with three other species.In conclusion, the interspecies differences were demonstrated with all the primers. Primers 1 and 2 were able, to some extent, to differentiate these species, while primers 1 and 3 separated P. frequentans from the others. Key words: Penicillium, molecular pattern, random amplified polymorphic DNA-polymerase chain reaction, molecular bands.