Trichoderma viride and Cladosporium herbarum were isolated from clay soil and irradiated with different doses of gamma radiation (0.5, 1, 1.5, 2 kGy). The inhibitory effect on growth rate was dose dependent with maximum inhibition at 1.5 and 2 kGy for T. viride which showed no growth. On the other hand, T. viride which grown on a medium contained aqueous extract from C. herbarum (gcae) showed resistance than that of the wild one and exhibited growth rate of 0.22 mm / day at 2 kGy. Cladosporium herbarum showed resistance to gamma radiation with a growth rate of a 0.62 mm / day after irradiation with 2 kGy. This indicated the presence of resistant factor/s in the extract of Cladosporium herbarum which utilized by T. viride. Therefore, molecular studies were carried out to detect any variation in the investigated fungi. Molecular studies revealed the presence of 57 bands and 41 polymorphic bands with a total polymorphism percentage of 71.92%. The number of polymorphic bands per primer ranged from 14 bands with polymorphism percentage of 73.68% for A01 primer, 16 polymorphic bands with polymorphism percentage of 84.21% for C02 to 11 bands with polymorphism percentage of 57.89% for B07 primer. Therefore, such average polymorphism might be due to the effect of different doses of gamma radiation. The study clearly showed the possibility of improving the capability of radiation sensitive fungi to be more resistant to radiation by growing them on extract from radiation resistant ones.