The present study evaluated the effect of dietary protein levels on growth performance and blood parameters of juvenile marbled spinefoot ( Siganus rivulatus). Five semipurified, isoenergetic (14.2 MJ digestible energy/kg; 84 g lipids/kg) diets were formulated to contain 30, 35, 40, 45, and 50 g crude protein (CP)/100 g diet. Groups of 15 juvenile fish (7.4 g individual weight) were randomly assigned in triplicate to each of the five treatments and offered the test diets three times daily ad libitum for 9 weeks. Total erythrocyte and differential leukocyte counts, hematocrit, hemoglobin, blood glucose, protein, and serum aspartate aminotransferase and alanine aminotransferase were evaluated. Survival was greater than 95% in all treatments. Maximum growth was observed in fish offered the diet containing 40 g CP/100 g diet crude protein. Differences in dietary protein level had no effect on the hepatosomatic and viscerosomatic indices of the fish, but whole body composition was influenced by diet. Blood parameters showed no physiological or metabolic dysfunctions among fish offered any of the five diets. Findings of the present work strongly suggest that diets containing 40 g CP/100 g and 14.2 MJ digestible energy/kg are suitable for good growth of juvenile spinefoot rabbitfish Siganus rivulatus and do not affect hematological parameters.