The aim of this study was to determine the effect on non-specific defence mechanisms in rainbow trout (Oncorhynchus mykiss) fed diets containing different doses of P-glucan (MacroGard), Schizosaccharomyces pombe and S. pombe P450. Over a period of 3 weeks, fish were given 0.1% and 1% MacroGard, 0.1% and 1% S. pombe, 0.1% and 1% S. pombe P450 in their food. Then phagocytosis, intracellular and extracellular respiratory burst activity, total protein, and specific growth ratio and condition factor values were determined. After feeding for 3 weeks with three different immunostimulants, extracellular and intracellular respiratory burst and phagocytic activity were significantly increased in the groups fed 1% MacroGard and 0.1% S. pombe P450 compared with the control group and the other experimental groups (P < 0.05). Respiratory burst activity was higher in all the experimental groups than in the control group. Phagocytic activity was elevated in all the experimental groups except that fed 0.1% MacroGard (P < 0.05). Total protein levels were higher in all the experimental groups than in the control group, but the difference was not significant (P < 0.05). The results indicate that rainbow trout fed different doses of MacroGard, S. pombe and S. pombe P450 all showed increased intracellular and extracellular respiratory burst activity, and phagocytic activity. However, there was no effect on total protein. In conclusion, S. pombe P450 could confer the same non-specific immunity as MacroGard.