Abstract: A strain with strong inhibitory activity against Aspergillus fumigatus named as LZ54， was isolated from the feces of infants by the overlay plate method. The strain was identified as Lactobacillus paracasei by physiological and biochemical characterization and 16S rDNA sequence nomology analysis. Some antimircrobial substances exist in the cell\|free fermentation supernatant were dealt with pH， enzymatic， Amberlite XAD\|2 macroporous resin， and it was observed the antifungal activity was high at the neutral acid pH， but the antifungal activity decreased rapidly with the increase of pH. After enzymatic treatment of supernatant with pepsase， trypsin and proteinase K， loss of part of the antifungal activity was observed， which indicated there were other proteinaceous substance with the antifungal activity. After dealing with the XAD\|2， the supernatant possessed the ability to inhibit Aspergillus fumigatus as well， and the molecular weight of the antimicrobial substance was about 5 kD determined by the SDS\|PAGE.

Key words: Aspergillus fumigatus, Lactobacillus paracasei, antimicrobial peptide