Numerous studies using Caenorhabditis elegans have used a protocol in which chemicals are orally delivered by incorporating them into the nematode growth media or mixing them with the food bacteria. However, actual exposure levels are difficult to estimate as they are influenced by both the rates of ingestion into the intestine as well as absorption from the intestinal lumen. We used liposomes loaded with the hydrophilic fluorescent reagent uranin to test oral administration of water-soluble substances to C. elegans. Ingestion of liposomes loaded with fluorescent dye resulted in successful oral delivery of chemicals into the intestines of C. elegans. Using liposomes, oral administration of hydrophilic antioxidants (ascorbic acid, N-acetyl-cysteine, reduced glutathione, and thioproline) prolonged the lifespan of the nematodes, whereas the conventional method of delivery showed neither fluorescence nor longevity effects. Our method efficiently and quantitatively delivers solutes to nematodes.