In the present work; the effect of whole body exposure of rats to mixed radiation (MR) from fast neutrons (FN) and 50Hz, 0.05mT magnetic field (MF) on the structural functions of the animal testis were investigated. For this; 100 white albino rats were divided equally into four groups namely A, B, C and D. Animals of group A were used as control, groups B and C were exposed to 50Hz, 0.05mT MF and fission neutrons from 252Cf source at a dose rate 10 μSv/h respectively for a period of 4 weeks at a rate of 8h/day and 5 days/week. Group D was exposed to fission neutrons and MF at the same field strengths and dose rates for the same period as groups B and C. At the end of the exposure period, blood was collected, animals were sacrificed and testes were removed for histopathological examination. The results indicated highly significant decrease (p<0.0001) of testosterone hormone level (THL) in blood for animals from all groups as compared to control. Moreover; highly significant increase (p<0.0001) in the creatine phosphokinase (CPK) enzyme in sera was measured for all exposed animals. Results were analyzed depending on the probable mechanisms of interaction of these types of radiation with biological tissue. It was concluded from the present findings that the induced damage of the testis and the dramatic elevated CPK enzyme levels are higher for exposure to mixed radiation as compared with exposure to a single field.