Abstract A novel antifungal protein, designated castamollin, was isolated from Chinese chestnut ( Castanea mollisima) seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM–Sepharose and FPLC-gel filtration on Superdex 75. Castamollin possessed a novel N-terminal sequence demonstrating little similarity to N-terminal sequences of Castanea sativa chitinase. Castamollin exhibited a molecular mass of 37 kDa in gel filtration and SDS–PAGE. It inhibited the activity of human immunodeficiency virus-1 reverse transcriptase with an IC 50 of 7 μM and translation in a cell-free rabbit reticulocyte lysate system with an IC 50 of 2.7 μM. Castamollin displayed antifungal activity against Botrytis cinerea, Mycosphaerella arachidicola, Physalospora piricola, and Coprinus comatus but was devoid of lectin activity.