Three new polyketides, (2S)-2,3-dihydro-5,6-dihydroxy-2-methyl-4H-1-benzopyran-4-one (1), (2'R)-2-(2'-hydroxypropyl)-4-methoxyl-1,3-benzenediol (2), and 4-ethyl-3-hydroxy-6-propenyl-2H-pyran-2-one (3) were isolated from the culture broth of Colletotrichum gloeosporioides, an endophytic fungus derived from the mangrove Ceriops tagal. The structures of 1-3 were elucidated on the basis of NMR spectra and HR-ESI-MS data. Their absolute configurations were determined by comparing with the experimental and calculated ECD spectrum. Compounds 1 and 3 showed potent antibacterial activities against some of the tested microbes.