The ultrastructure of the spore wall ofEncephalitozoon cuniculiwas studied using thin sections, freeze‐fracture and quick‐freezing deep‐etching techniques. The exospore was found to be very complex and to consist of three layers: an outer spiny layer, an intermediate electronlucent lamina and an inner fibrous layer. The intermediate lamina and the inner fibrous layer apparently are fibrillar. The spore wall is known to be chitinous and its fine structural appearance shows some structural similarities to other chitin containing structures.