The ylide (5-carboxypentyl)triphenyphosphonium bromide, which was widely used in the synthesie of stereo selectivity drug. 6-Bromohexanoic was synthesized withε-caprolaetone and hydrobromic acid over sulfuric acid, was synthesized via condensation with triphenylphosphine to produce (5-carboxypentyl)triphenyphosphonium bromide. The effect of reaction conditions on the properties of (5-carboxypentyl)triphenyphosphonium was investigated by method of experiments. The results show that the yield of (5-carboxypentyl)triphenyphosphonium could reach 82.2% and its content was 98.3% calculated by acetylacetone under the following reaction conditions: the molar ratio of ε-caprolaetone to triphenylphosphine and hydrobromic acid was 1.0∶0.95∶1.4, at reflux temperature, and the reaction time was 14 hours.