Pisum sativum defensin 1, an antifungal peptide isolated from pea seeds, has been shown to have strong in vitro activity against a variety of fungi. The 159bp cDNA enconding sequence for the mature Psd1 peptide was cloned into pGAPZaC vector to transform both X-33 and GS115 Pichia pastoris electrocompetent cells. Positive recombinant yeasts (confirmed by PCR technique and Zeocin selection) were cultured in small scale for protein expression and determination. Constitutive secretion of a recombinant 5kDa protein that is similar to native Psd1 was achieved as confirmed by SDS-PAGE and MALDI-TOF assays. Also, in vitro activity of rPsd1 against Neurospora crassa fungus confirmed its biological activity. We further evaluated biocontrol activity of P. pastoris strain constitutively secreting rPsd1 defensin against blue mold of apple in postharvest storage fruits. Blue mold of apple, caused by Penicillium expansum, has been one of the most important diseases in storage apple (Malus domestiva cultivar Golden Delicius) in USA. Biological control of fruit decay by natural antagonists has been the focus of several research groups once its acceptability by population seems to be greater than genetic manipulation or the use of pesticides. Once untransformed X-33 strain grew better than GS115 in Golden Delicious apple wounds, biological control tests were focused on X-33 transformants. The incidence of blue mold decay caused by P. expansum on fruits treated with the isolated fungus, in co-infected apples with the parent strain, with a transformant with the empty PGAPZaC plasmid or with the rPsd1 secreting strain was 100%, 56%, 33% and 11%, respectively, after 5 days of incubation at 24^oC. The consistency of this control still must be established. Supported by: CAPES, CNPq, FAPERJ and USDA.