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Longan pericarp proanthocyanidins (LPPs) were extracted and examined by structural and bioactive analyses. By 1H and 13C NMR spectra, LPPs were identified for the first time containing dominant catechin/epicatechin units with a mean degree of polymerisation of 3.3. Consistent with this result, electron spray ionisation (ESI) mass spectra revealed that the predominant LPPs were poly(epi)catechin with abundant A-type and B-type linkages. Matrix-assisted laser desorption ionisation time of flight (MALDI-TOF) mass spectra of LPPs showed dominant [M + Na]+ peaks that corresponded to procyanidin trimers–octamers. The presence of galloyl group in monomeric units of LPPs was confirmed by FT-IR, NMR, ESI and MALDI-TOF mass spectrometry (MS). Moreover, LPPs had a strong antioxidant activity of 1.23 × 104 µmol TE/g as measured by oxygen radical scavenging capacity (ORAC), and α-amylase inhibitory activity with IC50 for uncompetitive α-amylase inhibition of 0.075 mg/mL. These results indicate LPPs are promising antioxidant which could be applied as potential functional food components.