AbstractCrustacean and yeast cell wall chitin were analyzed by means of transmission electron microscopy and selected‐area diffraction. Single fibrils 8–25 nm wide have been observed in the micrographs of crustacean chitin. Analysis of a series of diffraction patterns obtained from thin crustacean chitin platelets yielded results which were in a better agreement with the theoretical structural model than those measured earlier. In this respect electron diffraction is shown to be superior to the more commonly used x‐ray diffraction. Yeast cell wall chitin had a less perfect structure than the crustacean chitin. Single fibrils were not observed on the micrographs and electron diffraction patterns did not show any preferred fiber orientation. The evaluation of electron‐diffraction patterns of both the primary septum and the adjacent circular zone of scar ring led to the conclusion that α‐chitin is present in both these parts of the mothe