In natural waters, the spawning reefs of Sepioteuthis lessoniana are mostly distributed in small rocks, broken shells and seaweed clumps, which interact with environmental pollutants. Therefore, certain deep studies have become extremely important to obtain insights into the adaptation of its structure and function to sophisticated environment during the breeding. Herein, the histological structure and cell type of the nidamental gland of adult S. lessoniana were observed by tissue slice techniques and transmission electron microscopy. The results showed that the surface of the nidamental gland was smooth and milky, with parallel lines on the surface (Fig. 1). and the nidamental gland was composed of three subdivisions: glandular wall tissue, secretory lobe and connective tissue. The glandular wall tissue was composed of the outer membrane layer and the muscular layer, which was located outside of the gland (Fig. 2a). The secretory lobe was the most important structure in gland and was layered (Fig. 2d). Connective tissue mainly existed in the junction of glandular wall tissue and secretory lobe, basement membrane of secretory lobe, and extracellular matrix between secretory cells (Fig. 2a﹣c). Further, the cell composition of the secretory lobes was dissected. The secretory lobes comprised two cell types, supporting cells and secretory cells (Fig. 3a). The supporting cells were small, oval in shape, located at the base of the secretory lobe, and the organelles in the cells were rare, and only a few mitochondria were observed (Fig. 3a, c). However, the secretory cells were large and rectangular with a large number of organelles, including mitochondria, endoplasmic reticulum and Golgi complex, visible in the cells (Fig. 3a, d, e). And we observed surprisingly few vesicles and protein vesicles, which were likely concentrated on the outside of the cell. Together, cilia were abundantly produced (Fig. 3b, f). We conclude that the nidamental gland is a typical secretory gland, and that primary function of the gel-forming substances is to form the third layer, which plays an essential role in protecting the fertilized egg against various environmental pollutants.