Hematological studies on fishes have assumed greater significance due to the increasing emphasis on pisciculture and greater awareness of the pollution of natural water resources. Such studies have generally been used as an effective and sensitive index to monitor physiological and pathological changes in fishes, especially in the management of endangered species. This study was undertaken to establish a reference range for six important blood serum enzymes. Serum samples of 40 Acipenser stellatus (20 female and 20 male) were analyzed, and serum enzyme values were determined. The reference ranges for the total samples and also for each sex were determined. The activities of measured enzymes in serum were: aspartate aminotransferase (AST) 265.60 ± 56.55 IU/l, alanine aminotransferase (ALT) 5.65 ± 1.18 IU/l, acid phosphatase (ACP) 15.63 ± 2.59 IU/l, lactate dehydrogenase (LDH) 2007.15 ± 521.97 IU/l, creatine kinase (CK) 6,596.05 ± 1,807.19 IU/l, and alkaline phosphatase (ALP) 69.05 ± 13.04 IU/l. There were significant differences between male and female fish in terms of AST and CK activity (P < 0.05). These may be related to the season of sampling and changing physiological cycles during spawning during which period the sexual hormones and stress are more obvious. However, there were no differences in the activity of ALP, ACP, LDH, and ALT between sexes. The correlations between measured enzymes were also determined.