Molecular profiles of PCR-RFLP and sequence analysis of internal transcribed spacer (ITS) regions of rDNA were compared between morphologically distinguishable species of Trichoderma isolated from substrates of oyster mushroom in Korea, T. atroviride, T. citrinoviride,T. harzianum, T. longibrachiatum, T. virens, and two unidentified species, Trichoderma sp. 1 and 2. PCRRFLP analysis divided the Trichoderma spp. into six RFLP groups, A, B, C, D, E, and F. The RFLP groups were generally agreed with described morphological species, except that the RFLP group A containing the two unidentified species. A neighbor-joining tree based on ITS sequences well supported RFLP groups observed by RFLP analysis of ITS regions of rDNA.Additionally, the two unidentified species, Trichoderma sp. 1 and 2, which could not be distinguished by PCRRFLP analysis, were separated in sequence analysis of ITS regions of rDNA.