Plants in Amorphophallus genus are rich in soluble dietary fibres and have long been used as food and traditional medicine in Asian countries. In the present investigation, natural O-acetyl-glucomannans were extracted from tubers of Amorphophallus rivirei (konjac), A. albus and two local types of A. bulbifer (wild type M and wild type B), which were designated as KGM, AGM, MGM, and BGM, successively. Comparative studies were conducted on their physicochemical properties and primary structures. The four AcGMs had about 90% (w/w) neutral sugar, 11% (w/w) moisture, and 1%–2% (w/w) ash. Relatively high contents of acetyl groups (17%–24%, w/w) were detected. Mannose and glucose as the main components existed in molar ratios of 1.41, 1.41, 1.21, and 1.58 for KGM, AGM, MGM, and BGM, respectively. Relative molecular weights of AcGMs increased in the order of: KGM