Methylated soy protein (MSP) which is positively charged with enhanced hydrophobicity may have antiviral action. This study is verifying if MSP can act inhibit H5N1 inside an animal model. Five groups of Hubbard chicks were challenged at the 25th day of the experiment with AIV virus (H5N1; 0.1 × 105 EID50/mL); 1 group did not receive any treatment (positive control), 2 groups (protective) received treatments before and after the challenge (0.1–0.2 g/L in drinking water ad libitum), and 2 groups (curative) received them only after the challenge. The positive control recorded 100% mortality after 3–5 days of infection. Chicken receiving MSP (0.2 g/L), delayed reaching to 100% mortality to the 7th day after infection, while those receiving MSP low level (0.1 g/L) could achieve 100% survival during the whole incubation period (42 days), either as a preventive or curative approach. H5N1 virus was not detected in the tracheal and cloacal swabs of the groups receiving 0.1 g/L, opposite to the positive control. The low level of MSP (0.1 g/L) reduced the viral titer to about 1% of the positive control in the protective and curative groups after 5 days of infection, and could maintain the bird body-weight, liver and kidney function, and histopathological status within the normal values. Humoral and TLC response in the group receiving both the virus and the MSP (0.1 g/L) may refer to a possibility that MSP-weakened virus has transformed into a vaccine-like material eliciting host immunity.