The structure determination of the title compound, rotenone alpha-oxime [systematic name: 1,2,12,12a-tetrahydro-8,9-dimethoxy-2-(1-methylethenyl)-[1]benzopyrano[3,4-b]furo[2,3-h][1]benzopyran-6(6H)-one oxime], C(23)H(23)NO(6), confirms that the molecule has an approximately V-shaped structure. One of the rings has a typical cyclohexene-like monoplanar conformation and the central ring adopts a 1,2-diplanar conformation.