Cocoons are a key life-history stage of leeches, so it is of great ecobiological significance to clarify their morphological features and chemical composition. Wuling cave leeches (Sinospelaeobdella wulingensis) are the type species of the newly-described genus Sinospelaeobdella, which breed on the roof wall of karstic caves, and differ from water and land leeches ecobiologically. In view of the particularity of Wuling cave leeches and the key role of cocoons in the adaptive evolution of leeches, morphology and chemical composi-tion of the cocoons were preliminarily studied. The results showed that: 1) Cocoons of Wuling cave leeches were roughly ellipsoidal, with a long diameter of (10.80±1.71) mm and a short one of (8.32±1.60) mm, and a weight of (135.3±76.8) mg; 2) From outside to inside, each cocoon had the outer layer (honeycomb) and in-ner layer of cocoon-wall, protein fluid and fertilized egg; 3) There were 17 kinds of hydrolyzed amino acids and 11 kinds of free amino acids in the cocoon, among which the relative contents of glutamic acid and ala-nine were the highest; 4) There were 68 kinds of trusted proteins identified in the cocoon, of which 27 were unidentified, and the remaining 41 could be divided into 6 categories, namely 5 antioxidant proteins, 12 en-zyme proteins, 6 cytoskeletal proteins, 12 binding proteins, 2 heat shock proteins and 4 other proteins. The morphological characteristics and chemical composition of the cocoons reflect long-term adaptation of leeches to cave ecological environments. The crucial role of the cocoon in the species evolution and population sur-vival of the leeches deserves further systematic investigation.