Abstract: iclofenac potassium delayed-sustained release pellets were prepared by double-layer coating method with ethylcellulose aqueous dispersion.The effects of release condition and pellet compositions on the in vitro drug release were evaluated.The formulation was optimized by the central composite design-response surface methodology.It was shown that the pH of the media greatly affected the in vitro drug release of the pellets while the viscosity of the media had little influence.Drug release from the pellets was related to the proportion of the inner coat to the outer coat and the amount of pore forming agent in the outer coat.The optimization of the formulation could be achieved by the central composite design-response surface methodology.