Four casssane diterpenes were isolated from the ethanol extract of the seeds of Caesalpinia decapetala (Fabaceae), with a combination of various chromatographic approaches, including silica gel, Sephadex LH-20, reverse phase C18 and so on. On the basis of spectroscopic data analysis, they were identified as caesalpinin MQ (1), neocaesalpin N(2), caesalmin F (3) and α-caesalpin (4). Among them, compound 1 is a new diterpene, compounds 2-4 were isolated for the first time from the plant of C. decapetala.