(+)- and (-)-Sinensilactam A (1), novel hybrid metabolites possessing a unique 2H-pyrrolo[2,1-b][1,3]oxazin-6(7H)-one ring system, were isolated from the fruit bodies of Ganoderma sinensis. The structures of these substances and absolute configurations at their stereocenters were assigned using spectroscopic and computational methods along with X-ray crystallographic analysis. A plausible pathway for the biosynthesis of 1 is proposed. (-)-1 was found to be a Smad3 phosphorylation inhibitor in TGF-β1 induced human renal proximal tubular cells.