The present study investigated the effect of Ficus carica polysaccharide (FCP), isolated from the fruit of F. carica L., at 0%, 0.1%, 0.5% and 1.0% doses supplementation with feed on genes Interleukin 1-β (IL-1β), Tumor Necrosis Factor α (TNF-α) and heat shock protein 70 (HSP70) gene expression in blood, humoral innate immune parameters and resistant to Flavobacterium columnare of grass carp at weeks 1, 2 and 3. The results revealed that administration of FCP significantly (P < 0.05) up regulated IL-1β and TNF-α gene expression. HSP70 gene expression was significantly (P < 0.05) lower in FCP-fed fish at the end of trial. The serum total protein, albumin and globulin did not significantly increased in any diet on the first week whereas it was significantly enhanced in 0.5% and 1.0% supplementation diets on weeks 2 and 3 when compared to control. The serum complement C3 was significantly (P < 0.05) increased on weeks 1 and 2 when compared to control, however, no significant difference was found in this activity after 3 weeks of treatment. All diets significantly enhanced the serum lysozyme activity, bactericidal activity from weeks 1–2 as compared to control. Grass carp fed with FCP showed remarkably higher resistance against F. columnare (60% survival) compared to the control group (30% survival). These results confirm that FCP can up regulate immune related genes expression, stimulates immune response that per se enhances disease resistance in grass carp.