Two tetranortriterpenoids, kokosanolide A (1) and C (2) were isolated from the seeds and three onoceranoid-type triterpenoids: kokosanolide B (3), 8,14-secogammacera-7,14-diene-3,21-dione (4) and a 1.5:0.5 mixture of 8,14-secogammacera-7,14(27)-diene-3,21-dione (5) and compound 4 were isolated from the bark of kokossan (Lansium domesticum). Complete 1H- and 13C-NMR data of the triterpenoids 1-5 are reported. The triterpenoids’ structures were elucidated primarily by means of high field 1D- and 2D-NMR, IR and HRMS spectral data. Triterpenoids 1-5 exhibited moderate to strong antifeedant activity against the fourth instar larvae of Epilachna vigintioctopunctata.