A novel lactam metabolite, 1-pentyl-8-oxa-3,6-diazabicyclo[3.2.1]octane-2,4,7-trione (1), was isolated from Penicillium sclerotium D35. The structure of the new compound 1 was elucidated by spectroscopic methods, including 1D and 2D NMR data and HR-MS. Compound 1 showed moderate nematode suppression activity with LC50 values of 344.722 mg/L.