Two new phloroglucinol derivatives, identified as anthuminoate (1) and anthuminone (2), were isolated from the ichthyotoxic ethyl acetate fraction of Syzygium polyanthum leaves. In addition, bioassay-guided fractionation followed by dereplication of the photocytotoxic fraction of this plant part has resulted in the identification of five known pheophorbides as the bioactive constituents. The compounds were identified as pheophorbide-a, methyl pheophorbide-a, methyl hydroxypheophorbide-a, pheophorbide-b and hydroxypheophorbide-b. Inhibition of cell viability shown by the compounds ranged from 83.3 to 86.1% at a test concentration of 5 microg/mL. This shows that Syzygium polyanthum leaves are a potential new source in the studies of photocytotoxicity for photodynamic therapy.