A feeding trial was conducted to investigate the effects of the dietary incorporation of autoclaved and raw (non-autoclaved) Ulva meal on juvenile rainbow trout (Oncorhynchus mykiss) growth, nutrient utilization, body composition, diet digestibility and fatty acid composition. An algae-free control diet and four experimental diets with either 5 or 10 % inclusion levels of raw Ulva meal (5 % = RU5; 10 % = RU10) or autoclaved Ulva meal (5 % = AU5; 10 % = AU10) were formulated. Fish were fed three times daily to apparent satiation for 12 weeks. The growth of fish fed RU10 (final weight = 76.7 +/- A 3.31 g; SGR = 2.8 +/- A 0.05 %) diet was significantly higher than that in fish fed the AU10 diet (67.5 +/- A 1.61 g; SGR = 2.6 +/- A 0.03 %). The feed conversion ratio (FCR) was significantly better in fish fed the RU10 diet (0.9 +/- A 0.06) compared with control diet (1.0 +/- A 0.06). Condition factor, viscerosomatic index and dress-out remained unaffected by dietary treatment. The hepatosomatic index (HSI) was significantly lower (P < 0.05) in fish fed the AU10 diet (1.2 +/- A 0.19) than fish fed the other diets (a parts per thousand yen1.6). The level of eicosapentaenoic acid (20:5n-3-EPA) in muscle from fish fed the RU10, AU5 and AU10 diets was significantly higher than in fish fed control diet (P < 0.05). Dietary inclusion of Ulva meals resulted in a significant increase in muscle docosapentaenoic acid (22:5n-3-DPA) levels at the end of the feeding period. The results indicate that the dietary inclusion of raw Ulva meal at levels of up to 10 % can be used without significant negative effects on the growth performance, nutrient utilization, dietary digestibility and muscle fatty acid composition. In fact, the inclusion of dietary raw and autoclaved Ulva meal elevated n-3 fatty acids levels of rainbow trout muscle.