In reverse genetics, RNA interference (RNAi) which is substitutable for gene-disruption, is an outstanding method for knockdown of a gene's function. In Caenorhabditis elegans, feeding RNAi is most convenient, but this RNAi is not suitable for knockdown of multiple genes. Hence, we attempted to establish an efficient method of feeding RNAi for multiple knockdown. We produced bacteria yielding three distinct double-stranded RNAs bound to one another, and fed those bacteria to C. elegans. Quantitative RT-PCR and observation of phenotypes indicated that our method is much more efficient than the traditional one. Our method is useful for investigating genes' functions in C. elegans.