Two new cassane diterpenoids, 14β-hydroxycassa-11(12),13(15)-dien-12,16-olide (1) and 6′-acetoxypterolobirin B (3), together with a known analogue, identified as 12α,14β-dihydroxycassa-13(15)-en-12,16-olide (2), were isolated from the fruits ofPterolobium macropterum. Compound1is a cassane diterpenoid with a Δ11(12)double bond conjugated with an α,β-butenolide-type, whereas compound3is a dimeric caged cassane diterpenoid with unique 6/6/6/6/6/5/6/6/6 nonacyclic ring system. The structures of1and3were characterized by extensive spectroscopic analysis combined with computational ECD analyses. The α-glucosidase inhibitory activity of isolated compounds was evaluated, and compounds1and3showed significant α-glucosidase inhibitory activity with IC50values of 66 and 44 μM.