The present study was designed and conducted in order to evaluate effects of different dietary betaine supplementation levels (0.5, 1, 1.5, 2 and 2.5 % Betaine kg^-1 diet) on the growth rate, carcass compositions and some haematological-biochemical parameters of the blood serum in beluga, Huso huso to do so, 150 individuals (4.6±0.61 g) were randomely distributed into 15 fiberglass tanks (500 liter, 10 individuals in each tank). Three replicates were considered for each treatment and the fish were fed by one of five experimental diets for 12 weeks. Final weight, specific growth index, protein efficiency ratio, condition factor (CF) and feed conversion ratio (FCR) were significantly more favourable in the fish fed by diets containing 1.5 -2 % Betaine kg^-1 diet compared to those fed by diets containing 0.5 % Betaine kg-1 diet at the end of experimental period. The higest growth performance and nutrient efficiency were also observed in the fish fed by diets containing 1.5-2 % Betaine kg^-1 diet. The level of protein in the carcass was significantly increased as a result of adding Betaine to the fish diet. The mean number of white blood cells (WBC), activity of liver enzymes such as Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST) were significantly lower in the fish fed by diet containing 1.5 and 2 % Betaine kg^-1 diet compared to those fed by 0.5 % Betaine kg^-1 diet. Consequently, it is suggested to use 1/5-2% Betaine in the food diet of juvenile beluga sinorder to obtain the maximum growth rate, optimized carcass composion, haematologicalparameters