Sideroxylonal C (3), a new phloroglucinol dimer, was isolated from the flowers of Eucalyptus albens through bioassay-guided fractionation. The structure elucidation was based on 1D and 2D NMR experiments, MS analysis, and comparison with sideroxylonals A (1) and B (2). Sideroxylonal C inhibited human plasminogen activator inhibitor type-1 at 4.7 microM without any significant effect on human tissue plasminogen activator.