In the course of our continuing search for bioactive constituents of Korean medicinal plants, we isolated five new oxylipins, chaenomic acid A-E (1-5), and six known ones (6-11) from the twigs of Chaenomeles sinensis. The structures of the new compounds (1-5) were determined by spectroscopic methods, including 1D and 2D NMR ((1)H and (13)C NMR, (1)H-(1)H COSY, HMQC, HMBC, and NOESY), olefin cross-metathesis, and LC/MS analysis. The known compounds (6-11) were identified by comparison of their spectroscopic data and specific optical rotation with the reported data. The isolated compounds (1-11) were tested for their inhibitory effects on nitric oxide production in lipopolysaccharide-activated murine microglial cells and for their cytotoxic activities against four human cancer cell lines (A549, SK-OV-3, A498, and HCT-15).