The ability of five fungal species belonging to two genera of Aspergillus and Fusarium has been examined in the microbial transformation of androst-4-ene-3, 17-dione (AD). Furthermore, the biotransformation of nandrolone decanoate (2) by F. fujikuroi has been studied. AD (1) was converted by cultures of Aspergillus sp. PTCC 5266 to form 11 alpha-hydroxy-AD (3) as the only product, with a yield of 86% in 3 days. Moreover, two hydroxylated metabolites 11 alpha-hydroxy-AD (3, 65%) and 7 beta-hydroxy-AD (4; 18%) were isolated in biotransformation of AD by A. nidulans. On the other hand, it was metabolized by F. oxysporum to produce 14 alpha-hydroxy-AD (5; 38%) and testosterone (6; 12%). Microbial transformation of AD by F. solani led to the production of 11 alpha-hydroxy-AD (3; 54%) and testosterone (6; 14%). AD was reduced at the 17-position by F. fujikuroi to produce testosterone in the yield of 42%. Finally, nandrolone decanoate was transformed by F. fujikuroi via hydrolysis and oxidation at the 17-position to produce two metabolites namely 17 beta-hydroxyestr-4-en-3-one (7, 25.4%) and estr-4-en-3,17-dione (8, 33%), respectively. The all metabolites were purified and subsequently identified based on their spectra data analysis and comparing them to the literature data.