Heritiera fomes is a mangrove tree which is widely distributed in the Sundarbans mangrove forest, Bangladesh. In this study, the EtOH extract of stem bark from H. fomes was shown to be rich in procyanidins. Trimeric, pentameric and hexameric procyanidins were identified in addition to highly polymeric material (average degree of polymerization 18-24). Bioactivity studies showed high DPPH radical scavenging and 15-lipoxygenase (15-LO) inhibiting activities of the bark extracts (EC50 = 19.4 +/- 1.7 and IC50 = 22 +/- 1 microg/mL, respectively) which could be ascribed to its high content of procyanidins. The procyanidins were also assayed as DPPH scavengers and 15-LO inhibitors, with EC50 and IC50 values in the range of 8-15 and 10-15 microg/mL, respectively. The bark extracts showed antibacterial activities against K. rhizophilia, S. aureus, B. subtilis and P. aeruginosa, as well. No toxicity was observed in the brine shrimp assay.