THE INHIBITORY effects of aqueous Egyptian garlic extract on growth and penicillic acid production of Penicillium hirsutum were established. Minimal inhibitory concentration (MIC) of the aqueous garlic extract was determined by the agar diffusion assay, which was 30 mg/ml. Growth of the fungus in broth containing higher concentrations of garlic extract (18 and 24 mg/ml) showed that sporulation was completely inhibited after 7 days of incubation or became very slight after 10 days at these mentioned concentrations. The increase in garlic concentration caused a gradual increase in the average values of mycelial dry weights reaching a maximum at 24 mg/ml. In the contrary, the increase in garlic extract concentration induced a reduction in the levels of penicillic acid production. The amount of penicillic acid in presence of 24 mg/ml of garlic was approximately 44% that of control culture filtrate after 10 days of incubation, however penicillic acid was not detected completely at the same garlic extract concentration after 7 days of incubation. This study was also extended to analyze and evaluate the percentage of the main components in garlic extract that may be responsible for these inhibitory effects, applying GC-MS chromatographic analysis. This is the first report on the inhibition of penicillic acid production by a natural substance as garlic extract.