This study investigated the effect of Sargassum angustifolium and Gracilaria pulvinata extracts on the growth performance, body composition, antioxidant status and gut microbiota of rainbow trout (Oncorhynchus mykiss) fry. For this purpose, 540 fry of rainbow trout (initial weight 0.23±0.04 g) were distributed in 12 fiberglass tanks. Fish were fed with experimental diets containing 500 mg kg-1 of Sargassum extract (SA), 500 mg kg-1of Gracilaria extract (GL) and 250 mg kg- Sargassum + 250 mg kg-1 Gracilaria extract (SA+GL). The control diet was a commercial diet without seaweed extract. At the end of experiment growth and feeding performance including final weight, specific growth rate (SGR), weight gain (WG) and feed conversion (FCR) in all treatments were not significantly different (p > 0.05). Whole body protein, ash and moisture contents of fish were not significantly affected by dietary macroalgae extracts (p > 0.05). However, lipid content was significantly lower in fish fed of extract Gracilaria and Sargassum compared to control (p < 0.05). The seaweed extract-fed fish utilized efficiently the body lipid and suppressed body weight loss during starvation. No significant difference (p > 0.05) in serum total protein, creatinine alanine transaminase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and blood superoxide dismutase (SOD) activity were observed in all treatments. Whereas serum albumin, glutathione peroxidase (GPX) and catalase specific activity were higher in SA, GL and SA+GL treatments compared to the control group (p < 0.05). ACH50 level was significantly (p > 0.05) increased in GL and SA+GL treatments as compared SA and control group. The addition of Sargassum and Gracilaria extracts to feed did not affecte total bacterial population but increased lactobacillus bacteria levels (p < 0.05) in the intestine. These results revealed the potential antioxidant enhancing and health-promoting effects of dietary Sargassum angustifolium and