A new practical method is described for the synthesis of (Z)-7-eicosen-11-one (1) and (Z)-7-nonadecen-11-one (2), the active principles of the sex pheromone of the peach fruit moth. Lithium anion of 1-octyne (from acetylene and 1-bromohexane) was alkylated with 3-bromo-1-propanol tetrahydropyranyl ether and deprotected to afford 4-undecyn-1-ol, which was oxidized with pyridinium chlorochromate to 4-undecyn-1-al. 4-Undecyn-1-al was treated with 1-nonylmagnesiumbromide or 1-octylmagnesiumbromide to yield 7-eicosyn-11-ol and 7-nonadecyn-11-ol. Jones oxidation, followed by Lindlar catalytic hydrogenation afforded the target compounds. Biological activity of the synthetic pheromones as attractants for males of the peach fruit moth was tested in the field using polyethylene capsules as containers. For each vial containing about 3.0 mg of the synthetic pheromone, the number of trapped moths were counted.