The pressure is one of the most important factors affecting the microparticle formation when using the techmique of solution enhanced dispersion with supercritical fluids (SEDS).The relation between the microparticle's diameters of ethylcellulose and the pressure is studied,and the influences of pressure on the characteristics of amoxcillin-ethylcellulose-carbopol particles are investigated as well.It can be concluded that the diameters of the ethylcellulose microparticles and the sustained-release and adhesive drug particles decrease with the increase of pressure,but the drug contents and drug release curves are almost the same under two different pressures.