The insulin/insulin-like growth factor-I signaling (IIS) pathway regulates larval diapause, adult lifespan, fat metabolism, and stress-resistance in the nematode Caenorhabditis elegans. One of 38 C. elegans insulin-like genes, ins-11, was disrupted and phenotypic analyses of the gene-disrupted animal were performed. The gene-disruption exhibited a significant influence on the adult lifespan. It antagonized the lifespan extension induced by RNAi knockdown of another insulin-like gene, ins-7. Hence ins-11 appears to be necessary for lifespan extension caused by a decrease in the IIS pathway. This is the first description of gene-disruption of the C. elegans insulin-like gene that suppresses the lifespan extension.