Four new maleimide derivatives, antrocinnamomins E–H (1–4, resp.), together with (3S,4R)-1-hydroxy-3-(4-hydroxyphenyl)-4-(2-methylpropyl)pyrrolidine-2,5-dione (5) and ergosterol were isolated from the mycelia of Antrodia cinnamomea BCRC 36799. The structures were elucidated by 1D- and 2D-NMR spectroscopy, and mass spectrometry. Compounds 1–5 were evaluated for their inhibitory effects on nitric oxide (NO) production by macrophages. Compounds 2 and 4 showed stronger inhibition of NO production than the positive control quercetin.