Achyranthes aspera, an Indian medicinal plant (family: Amaranthaceae) was incorporated in artificial fish diet, and fed to catla Catla catla. After 4 weeks of feeding, fish were immunized with bovine serum albumin (BSA), spleen and blood were sampled on weekly intervals for four times after immunization. Antigen-specific antibody level in serum was determined by ELISA. Antigen clearance was determined in spleen by immuno-electron microscopy. Achyranthes has significantly (P < 0.05) enhanced the BSA-specific antibody titers than the untreated control group throughout the study period. The efficiency of antigen clearance was also enhanced in C. catla treated with Achyranthes.