The prospective effect of riboflavin (vitamin B2) to enhance the immune status of the Nile tilapia (Oreochromis niloticus) was investigated. Fish were divided into 4 groups before feeding for 2 weeks with  0, 10, 15, and 20mg/ kg of riboflavin. Some humoral immune parameters such as antiproteases, lysozyme, bactericidal, IgM, IL-12, total protein, and globulin, as well as hematological parameters (red and white blood cell counts) were estimated. The results revealed enhancement in all the humoral immune parameters of fish groups fed diets supplemented with riboflavin compared to the control fish, especially with the 10mg/ kg dose which recorded the highest significant increase (P< 0.05) in some parameters like antiproteases, lysozyme, bactericidal, and IgM compared to the control. In addition, the group that received 10mg/ kg of riboflavin recorded the highest significant number of the red blood cells (P< 0.05). A significant increase in number of  white blood cells (P< 0.05) was observed in 10 and 20mg/ kg treated groups. The current study suggests adding riboflavin to the diet, particularly at a 10mg/ kg dose, since it may be an effective food additive for enhancing the haematological and immune status of the Nile tilapia and increasing its resistance to disease.