It is widely accepted that chitin is present in nematodes. However, its precise role in embryogenesis is unclear and it is unknown if chitin is necessary in other nematode tissues. Here, we determined the roles of chitin and the two predicted chitin synthase genes in Caenorhabditis elegans by chitin localization and gene disruption. Using a novel probe, we detected chitin in the eggshell and discovered elaborate chitin localization patterns in the pharyngeal lumen walls. Chitin deposition in these two sites is likely regulated by the activities of chs-1 (T25G3.2) and chs-2 (F48A11.1), respectively. Reducing chs-1 gene activity by RNAi led to eggs that were fragile and permeable to small molecules, and in the most severe case, absence of embryonic cell division. Complete loss of function in a chs-1 deletion resulted in embryos that lacked chitin in their eggshells and failed to divide. These results showed that eggshell chitin provides both mechanical support and chemical impermeability essential to developing embryos. Knocking down chs-2 by RNAi caused a defect in the pharynx and led to L1 larval arrest, indicating that chitin is involved in the development and function of the pharynx.