Through our screening for new natural compounds, two 3,4,5-trisubstituted N-methyl-2-pyridone alkaloids, fusapyridons A (1) and B (2), along with the known compounds sambutoxin (3), Ndemethylsambutoxin (4), (-)-oxysporidinone (5), and the dimethyl ketal of oxysporidinone (6) were isolated from the fermentation extract of Fusarium sp. YG-45. Their structures were determined by spectroscopic analyses including NMR, MS, UV and IR. Compound 1 showed antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus.