This study was performed to evaluate the effect of dietary chitosan on haematology, innate immunity and protection against Vibrio anguillarum in Asian seabass, Lates calcarifer. A basal diet supplemented with 0, 5, 10 and 20 g chitosan kg−1 diet was fed to the four different groups for 60 days. The haematological (total erythrocyte count, total leucocyte count, total serum protein, albumin, globulin and albumin-globulin ratio) and innate immune parameters (phagocytic ratio, respiratory burst, serum lysozyme and serum bactericidal activities) were monitored at fortnight interval to assess the effect of chitosan feeding in Asian seabass. All the studied haematological and innate immune parameters were increased significantly (P ≤ 0.05) in chitosan-fed groups in comparison with control. However, the group fed diet containing 10 g chitosan Kg−1 feed showed highest haematological and innate immune parameters on 45th day in comparison with other groups. Moreover, the fish fed the diet containing 10 g chitosan Kg−1 feed had significantly higher post-challenge survival (75.56 ± 4.44%) on the 30th day following V. anguillarum challenge. Therefore, this study suggests that chitosan at 10 g kg−1 diet could be used as prophylactic in Asian seabass culture to enhance the protection against any possible infection by V. anguillarum.