The C‐type lectins mediate nonself recognition in insects. The previous studies focused on host immunlectin response to bacterial infection; however, the molecular basis of immunlectin reactions to endoparasitoids has not been elucidated. The present study investigated the effect of parasitization by Campoletis chlorideae on hemagglutination activity (HA; defined as the ability of lectin to agglutinate erythrocytes or other cells), and transcriptional expression of C‐type immunlectin genes in the larval host, Helicoverpa armigera. Parasitization induced four‐ to eightfold higher HA in the parasitized larvae, compared to nonparasitized larvae at days 2 and 6 postparasitization (PP), however inhibited HA at other days PP. Eight C‐type lectins were differentially expressed in different host developmental stages, from feeding to wandering stage. The mRNA levels of HaCTL1, HaCTL3, HaCTL4, and HaCTL5 were upregulated and HaCTL2 and HaCTL7 were downregulated. Tissue analysis showed that HaCTLs were mainly expressed in fat body or hemocytes, while HaCTL5 was highly expressed in testes. The effects of parasitization on the lectin expression patterns differed. Lectins except HaCTL6 or HaCTL5 were significantly down‐ or upregulated in parasitized larvae at day 4 or 6 PP compared with that of nonparasitized larvae. We infer from our results that C‐type immunlectins are involved in host–parasitoid interactions, and parasitization alter host immunlectin levels both in inhibiting and promoting host immune defenses to endoparasitoids. These immunlectin genes indicated an altered physiological status of the host insect, depending on developmental stage, tissue, and parasitization.