Semicontinuous supercritical antisolvent (SAS) precipitation has been employed for the production of micro- and nanoparticles of amoxicillin with controlled size and size distribution. Different mean sizes and size distributions of particles were achieved depending on the parameters of pressure, solution concentration, and organic solvent. The formed particles were spherical, separate, and of size between 0.2 and 1.6 mu m. The particles were successfully precipitated from a dimethyl sulfoxide (DMSO) solution and an ethanol/DMSO solution. In our study, high pressures and a coaxial nozzle for the introduction of the organic solution and the SAS were employed, resulting in the increased mixing of the two flows. The precipitated microparticles were analyzed with scanning electron microscopy. X-ray diffraction analysis of amoxicillin microparticles revealed that they become amorphous after SAS treatment. An attempt was made for the explanation of the influence of the different process parameters on the morphology, the mean size, and the size distribution of the precipitated particles.