In the course of searching for new antifungal agents, a new pentanorlanostane derivative, cladosporide A(1), was isolated along with ergosterol, ergosterol peroxide and 23, 24, 25, 26, 27-pentanorlanost-8-ene-3β, 22-diol(2) form Cladosporium sp. as a characteristic antifungal agent against the human pathogenic filamentous fungus Aspergillus fumigatus. The structure of 1 was established as 3β, 22-dihydroxy-23, 24, 25, 26, 27-pentanorlanostane-29-al by spectroscopic and chemical investigation and X-ray crystallographic analysis. Inhibitory activity against A. fumigatus (IC₈₀0.5-4.0 μg/ml) was observed for cladosporide A (1), but bo activity was observed against pathogenic yeasts, Candida albicans and Cryptococcus neoformans, and other parhogenic filamentous fungi, Aspergillus niger and A. flavus. The 4β-aldehyde residue in 1 might be essential for the antifungal activity, since 23, 24, 25, 26, 27-pentanorlanost-8-ene-3β, 22-diol (2) showed no inhibition against the above four fungi.