The purpose of this study was to determine changes in hematological and plasma indices of Common Carp Cyprinus carpio with regard to age, sex and hormonal treatment. Sixty fish were used to assess the age factor. Also, 20 fish including female and male were assigned to determine blood indices with regard to sex and hormonal treatment. The pituitary gland extract was used as hormone for males and females. Red blood cell (RBC), white blood cell (WBC), hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), calcium, glucose, cholesterol, triglyceride, protein and phosphorus showed significant differences among ages. However, hematocrit (HCT), lymphocyte and neutrophil did not show significant differences. Statistical analysis revealed that males had higher values of RBC, Ht, Hb, MCV, MCH, lymphocyte, neutrophil and cholesterol compared to females. Some hematology and plasma indices influenced both sexes before and after hormonal treatment. These results provide useful information for monitoring changes in the health status of fish.