Six known compounds, isoroquefortine C (1), griseofulvin (2), ergosterol peroxide (3), 3β-hydroxy-(22E,24R)-ergosta-5,8,22-trien-7-one (4), cerevisterol (5) and (22E,24R)-6β-methoxyergosta-7,22-diene-3β,5α-diol (6), were produced by the fungus Penicillium brasilianum, and their structures were elucidated by spectroscopic methods. This is the first report on isoroquefortine C as naturally occurring compound. Their bioactivities against five phytopathogenic fungi (Gibeberalla saubinetti, Fusarium solani, Botrytis cinerea, Colletotrichum gloeosporioides and Alternaria solani) and four pathogenic bacteria (Escherichia coli, Bacillus subtilis, Staphyloccocus aureus and Bacillus cereus), as well as allelopathic activities on Raphanus sativus were tested. Compound 1 exhibited a remarkable antifungal activity with minimum inhibitory concentration (MIC) of 12.5 μM against C. gloeosporioides, in comparison with positive control hymexazol (MIC 25 μM). Compound 2 displayed strong inhibitory effects on the growth of A. solani and S. aureus with MIC of 3.13 μM for each. Compounds 2 and 3 displayed a significant growth-inhibition activity on R. sativus.