The present paper deals with the morphology of the olfactory organs of the skates, rays and chimaeras, in correlation with the classification and ecology. Anato- mical investigations had been carried out in 42 species belonging to 25 Genera. 17 Families, 5 Orders and 2 Subclasses.According to the size of the opening and diameter of the olfactory sac, they all belong to the cup-shaped pattern, usually the opening of the olfactory sac is larger or at least 2/3 to the long diameter of the sac. They can be divided into 3 subpatterns, e. g. 1) Elliptical subpattern as in most skates and rays, 2) Broad and compressed, kidney-shaped subpattern, as in Rhinopteridae and Mobula (fig. 12, 13), 3) Rosetteshaped subpattern, the rachis is broad in the middle of the sac and the primary lamellae are arranged in rosette shape, such as in chimaeras. The primary lamellae in the former two subpatterns are arranged in pinnate parallel shape.Detailed measurements show that the olfactory epitbelium grows by increase in size and number of primary and secondary lamellae. The number of primary and secondary lamellae in same species and same size of different individuals are almost similar. The number of secondary lamellae are numerous in the middle portion of the olfactory sac and gradually decrease to each side (Table 1,2). The shape of secondary lamellae have 3 patterns, viz. 1) needle-shaped; 2) leaf-shaped; 3) double-leaf shaped.The skates and rays are called "Olfactory fishes", they possess particular acute sense of smell; the olfactory organ is more important than the visual organ. According to taxonomical and ecological features they are divided into 3 groups: 1)in Pristidae, Rhynchobatidae, Rhinidae, Rhinobatidae the dorsal and caudal fins are well developed and the tail portion strong. They have no nasoral groove, anterior nasal flap less developed, the nostrils are almost entirely exposed, the olfactory tentacles are very short, the inner wall of the olfactory sac and the free edge of primary lamellae bear numerous placoid scales, which can prevent objects entering into nostrils to damage the lamellae. The current of water through the olfactory sac is induced by the forward motion of the sawfishes and guitarfishes. Their primary lamellae are numerous. 2) in Rajidae, Urolophidae, Dasyatidae, Gymnuridae the inner margin of anterior nasal flap is joined across a broad isthmus in front of mouth and expanded rearward on either sde as an extended curtain, the expossed nostrils are small and have nasoral groove. The tentacles on the upper free side of primary lamellae are well developed, those on the anterior side near incurrent opening are larger and longer than those on the posterior side. The current of water passing through the olfactory sac is induced by the movement of tentacles. The number of primary lamellae are very few, and in the Torpediniformes being the fewest. 3) in Myliobatidae, Aetobatidae, Rhinopteridae and Mobulidae, they can "fly" swiftly in the water. The inner nasal valve is well developed in Aetobatidae and Rhinopteridae. The current of water through the olfactory sac is induced by the forward motion of the rays, and by movement of tentacles. The number of primary lamellae is 126—216 in Myliobatidae and Aetobatidae but in Mobulidae 242—254.