The seeds of Citrus reticulata afforded the new limonoid derivative, isolimonexic acid methyl ether, in addition to the previously isolated limonin, deacetylnomilin, obacunone and ichangin. The structure elucidation was achieved primarily through 1D and 2-D-NMR analyses. The marginal antimalarial activity of isolimonexic acid methyl ether is reported.