The methanolic extracts from the wood and bark of Cotylelobium melanoxylon were found to inhibit plasma glucose elevation after sucrose loading in rats and triglyceride elevation after olive oil loading in mice. A new stilbene dimer, melanoxylin A, together with the known stilbene dimers [(+)-ampelopsin F, (+)-isoampelopsin F, and (+)-epsilon-viniferin] and a trimer (vaticanol G) and a lignan [(+)-lyoniresinol] were isolated from the wood extract, and a new stilbene trimer, melanoxylin B, together with the known stilbene dimers [(+)-epsilon-viniferin and cis-(+)-epsilon-viniferin] and trimers (vaticanols A, E, and G) were isolated from the bark extract of C. melanoxylon. The principal constituents, vaticanols A, E, and/or G, inhibited plasma glucose and triglyceride elevation after sucrose loading in rats and olive oil loading in mice, respectively. In addition, vaticanols A, E, and/or G inhibited the enzyme activities of rat intestinal alpha-glucosidase, porcine pancreatic lipase, and rat lens aldose reductase.