Corosin (8; R = R 1 = H) has been reisolated through a modified procedure, as its acetate (8; R=H, R 1 = Ac), in an overall yield of 0.2% from jute roots. On pyrolysis in vacuo, corosin gave pyro corosin (1a; R 1 = OH, R 2 = COOH, R 3 = R 5 = H, R 4 = R 6 = Me), shown to have a 12:18 (17) di-ene formed by elimination of the 19-OH and the angular C-28 carboxyl in the molecule. On rearrangement with concentrated sulphuric acid in acetic acid, corosin acetate gave corosin anhydro lactone acetate (7; R 1 = Ac, R = H), having a 13(18) double bond and a lactone bridge between the 28-carboxyl and the 20-carbon atom. Corosin acetate ester (8; R = Me, R 1 = Ac), on treatment with sulphuric-acetic acid reagent, gave as the main product anhydro corosin acetate ester (7; R = Me, R 1 = A c), with a 12:18(19)-diene. The structure of corosin is proposed to be urs-12-ene-2α, 3β, 19α-trihydroxy-24, 28-dioic acid (8; R = R 1 = H).