Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt E-mail: madleneli@hotmail.com Manuscript received 4 January 2000, revised 24 August 2000, accepted 12 February 2001 A simple sensitive potentiometric method has been developed for determination of active haloester. It is based on the reac­tion of haloester with excess piperidine in ethanol at 40°. Under the optimum conditions the average recovery is 97%. The reaction proceeds kinetically as a pseudo-first order reaction. The reactivity of tested amines towards haloester follows the order : benzylamine < n-butylamine < ethylamine < piperidine. The activation parameters have been calculated and relevant reaction mechanism has been suggested.