RNA interference (RNAi) is a commonly used technique for reverse genetic approaches in Caenorhabditis elegans. Feeding RNAi is the most convenient and inexpensive method for performing genome-wide RNAi screens. However, it has been reported that knock-down of two genes (double RNAi) by feeding RNAi using a mixture of bacteria that each contained one dsRNA species produced poor results. To overcome this problem of inefficiency, we designed and tested a double feeding RNAi method using a single RNAi construct containing two gene fragments. From experiments with three different sets of genes, we found that the new double RNAi method consistently produced significantly enhanced double knock-down phenotypes. The double feeding RNAi approach described here provides a method to consistently examine phenotypes caused by depletion of more than one gene in C. elegans.