To isolate and characterize an antifungal peptide from the seeds of Brassica parachinensis L.H.Bailey. An antifungal peptide designated as brassiparin was isolated. It exhibited a molecular mass of 5716 Da. It potently inhibited mycelial growth in a number of fungal species including Fusarium oxysporum, Helminthosporium maydis, Mycosphaerella arachidicola and Valsa mali. The antifungal activity of brassiparin toward M. arachidicola exhibited pronounced thermostability and pH stability. It inhibited proliferation of hepatoma (HepG2) and breast cancer (MCF7) cells and the activity of HIV-1 reverse transcriptase. Its N-terminal sequence differed from those of antifungal proteins which have been reported to date. Brassiparin can be purified by using a protocol involving ion exchange chromatography, affinity chromatography and gel filtration. It manifests potent, thermostable and pH-stable antifungal activity. It demonstrates antiproliferative activity toward tumour cells, and inhibitory activity toward HIV-1 reverse transcriptase. Thus, brassiparin is a defense protein. Brassiparin represents one of the few antifungal proteins reported to date from Brassica species. Its antifungal activity has pronounced pH stability and thermostability. Brassiparin exhibits other exploitable activities such as antiproliferative activity toward hepatoma and breast cancer cells and inhibitory activity toward HIV-reverse transcriptase.