Due to the growing production and usefulness of magnetic nanoparticles in biological systems, so far fewer studies on the effects of these substances in living bodies have been. Determining factors of anemia and CBC in addition to any organism as a physiological index is important in diagnosis can help us. 200 numbers of common carp weighing 100 g were obtained from the Caspian Sea into the bucket with a capacity of 80 liters. In this study, the effects of three doses of iron oxide nanoparticles (0.01, 0.003, 0.006 mg/litr) along with control (no iron oxide nanoparticles) after time (48, 96, 120, 168 hours) the red blood cells of fish Cyprinus carpio was. Results showed that the mean number of red blood cells in a dose treatments of 0.003 and 0.006 increase. But a dose of 0.01 red blood cells is reduced and the largest number of red blood cells in a dose of 0.003 and 0.006 was observed after 168 hours, the number of red blood cells in the control group, the number 75 has been reported, but at a dose of 0.003, 0.006 to 210 has risen to 250. Has increased by approximately 75% (approximately 3 times the number of red blood cells), but a dose of 0.01, 60 is the number of red blood cells. The effect of iron oxide nanoparticles on the male than the female and immature fish were more females.