In recent years, immunostimulants have become a new research field in aquaculture. -glucan is one of the most important immunostimulants, which can enhance the body's resistance to infection by improving the non-specific and cellular immunity of animals. The present study evaluated the effects of different dietary -glucan dosages (0, 0.05%, 0.1%, and 0.2%) on the anti-infection ability of rainbow trout () after 42 days of feeding. Thereafter, rainbow trout were infected with and sampled on the 2nd, 4th, and 6th days post-infection. Survival rates as well as the regulatory processes of serum stress-related factors were analyzed. Survival rates in the -glucan groups increased significantly compared with those in the control group after P<0.05). On the 4th day after infection, the serum total protein concentrations in all -glucan groups were significantly higher than those in the control group (<0.05). Serum malondialdehyde activity in the 0.1% and 0.2% groups reached a peak on the 2nd day post-infection, which was earlier than in the other infected groups. The activity of serum myeloperoxidase in the 0.1% and 0.2% groups increased significantly after infection, whereas in the 0.05% and control groups, it decreased significantly (-glucan groups after infection was significantly lower than that in the control group (-glucan groups increased more obviously than those in the control group (<0.05). On the 4th day after infection, the serum urea nitrogen concentration in all -glucan groups was markedly lower than that in the infected control group (<0.05). Total bilirubin (T-BIL) concentration decreased significantly after infection; however, T-BIL in the 0.2% group was clearly higher than that in the other groups. After infection, expression in the liver and spleen in all groups increased significantly. In the 0.1% and 0.2% groups, it reached a higher peak earlier than in the control group. Overall, the liver and head kidney in rainbow trout were damaged to a certain extent after infection with -glucan can effectively protect fish from damage caused by -glucan showing the best effect.