Angelfish (Pterophyllum scalare, 1.54 +/- 0.03 g, n=500) were exposed for 24, 48, 72 and 96 hours to different concentrations NH3-N (0.2-2 mg/L), and NO2-N (1-35 mg/L) at pH 7.2 +/- 0.3. Using Probit analysis, 50% lethal concentrations (LC50) and 95% confidence limits were calculated. The effects of ammonia (0.7 mg NH3-N/L and 10 mg NO2-N/L) nitrite to the red blood cells size were also investigated in this study. As a result of the study, 24, 48, 72 and 96 hours LC50 values of ammonia nitrogen (NH3-N) for angelfish were determined as 0.99, 0.75, 0.65 and 0.58 mg/L; and nitrite nitrogen (NO2-N) values were calculated as 29.38, 12.30, 7.98 and 6.28 mg/L. respectively. In the examination of blood smear, red blood cells were determined oval shaped (erythrocytes and its nuclei size), and their sizes were measured and evaluated as long and short axes. It was also determined that, exposed to ammonia and nitrite, erythrocyte morphology had changed that was statistically different from each other (P<0.05).