The aim of this study was to compare some biochemical blood parameters of rainbow trout (Oncorhynchus mykiss) living in running or still waters. Some biochemical parameters of rainbow trout were examined, and the results were evaluated between sampling locations and according to seasonal changes. Healthy adult rainbow trout were caught from six different locations on the Bahçelik Dam Lake and the Zamantı River (Turkey). Blood samples were collected from the caudal vena cava and transferred to sample tubes. The blood serum samples were analyzed for 16 different biochemical parameters. In terms of the calculated blood parameters, no statistically significant differences were found between locations. However, seasonal changes affected the blood parameters significantly. alanine transaminase (ALT)was considerably higher in spring in fish caught from both the dam lake and the river. In the summer, aspartate transaminase (AST), Ca, urea, total protein and Fe were significantly higher than in other seasons. However, amylase was significantly lower in summer than in the other seasons. In the autumn, alkaline phosphatase (ALP) and triglyceride were significantly higher than in the other seasons. The results obtained from this study may be useful for research in fish biology and food safety