In our survey for antifungal compounds, a fermentation broth of Streptomyces sp. HA81-2 was found to inhibit the in vitro growth of Aspergillus fumigatus IFO 5840 accompanied by hyphal morphological abnormalities. One of the isolated antibiotics was identified as phoslactomycin E based on LC-MS and NMR spectral data. In a preliminary assay using the membrane fractions of A. fumigatus, phoslactomycin E was found to inhibit the activity of 1,3-beta glucan synthase.