Objective:To prepare 5 ASA colon specific targeting pellets by using aqueous dispersion coating process.Methods:5 ASA colon specific targeting enzyme controlled release pellets was prepared by a fluid bed coater,using ethylcellulose aqueous dispersion(Surlease) and Amylose as the controlled coating meterials,using diethyl o phthalate as the plasticizer.Its dissolution rate in vitro was studied in simulating gastrointestinal circumstances and adding the colon enzyme.The digestibility of free coating film was also studied in simulated colon circumstances.Results:Data obtained showed that the pellets were not released in upper gastrointestinal juice,however,over 80% of them were released in 3h in simulated colon circumstances and completely released within 10h.Drug release was due to the decomposition of amylose in the coating membrane by colon enzyme.The thicker the membrane and the more the amount of Surlease,the longer the lag time.The mechanism of release has been confirmed by digestibility of the free coating film.Conclusion:The colon specific targeting enzyme controlled release pellets could be prepared by adding amylose that can be decomposed by a colon specific enzyme,to the coating solution.