Abstract: This study was investigated the effects of waterborne lead (Pb) and calcium (Ca) dietary on Nile tilapia (Oreochromis niloticus) using hematology, micronucleus (MN) and nuclear abnormality (NA) analysis. The values of 96 h LC50 of Pb to tilapia in our laboratory was 182.38 mg L-1. Therefore, lead concentration tested in this sub-lethal experiment was 45 mg L-1 (correspond to 25% of the 96 h LC50). The dietary supplement with 0, 20 and 60 mg Ca2+ g-1 fish food were feeding for 30 days. Sixty fish were equally divided into six groups (G1: normal diet and water; G2: normal diet and waterborne lead; G3: low Ca2+ diet and water; G4: high Ca2+ diet and water; G5: low Ca2+ diet and waterborne lead; and G6: high Ca2+ diet and waterborne lead). After 30 days treatment, blood collection for hematology, MN and NA analysis. It was observed that, fish showed significant sensitivity to the different treatments. The results of hematological analysis including, hematocrit, hemoglobin, erythrocytes and leukocytes counts, were increased in Pb exposure when compare those of the control group, but no statistically significant. The percentages of immature erythrocyte count were increased from 1.1 to 3.8% through Pb exposure. NA shapes in erythrocytes were scored into blebbed nuclei (BL), lobed nuclei (LB), notched nuclei (NT) and binuclei (BN). In general, the highest value of both MN and NA cells were significantly increased in the Pb treated group followed by the combination of Pb and Ca2+ treated group. The frequencies of each NA shape in erythrocytes of all treatments were observed in the following NT>LB>BN>BL. Our results demonstrated the efficacy of calcium in reducing toxicity in fish induced by waterborne lead.