In order to investigate the alternation in serumic levels of creatinine, urea and uric acid in rainbow trouts (Oncorhyncus mykiss) affected by nephrocalsinosis, samples were taken during the winter of 1385 from three fish farms with different water sources of river, spring and well water recirculation system. Five samples were taken from each of the 8 different weight groups and a total of 120 specimens were collected randomly. After collecting the specimens, blood and renal tissue sampling was performed on all the fish with the tissue samples fixed in 10% buffered formalin and the separated sera stored at -200C for further evaluations. Renal Samples were transferred to the pathology laboratory and tissue sections were prepared and stained with hematoxylin and eosin. From the 120 collected specimens, 6 were affected by nephrocalcinosis with histopathologic evidence of severe dilation of renal tubules, presence of dense basophilic materials inside the dilated tubules and hyaline cast formation in some renal tubules. Amongst the 6 cases with nephrocalcinosis, 3(2.5%) were from the farm with well water recirculation system, 2 (1.66%) from the farm with river water supply and 1 (0.83%) from the farm which used the spring water source.  Evaluation of the amounts of urea, creatinine and uric acid indicated that there was a significant difference in mean creatinine levels between different weight groups (P< 0.05). In conclusion, according to the results of this study there is only a significant statistical difference in the amount of creatinine between healthy fish and those affected by nephrocalcinosis in each farm.