The micronization of an anticancer compound (5-Fluorouracil) by supercritical gas antisolvent (GAS) process was investigated. 5-Fluorouracil was dissolved in dimethyl sulfoxide (DMSO) and subsequently carbon dioxide as an antisolvent was injected into this solution thus, the solution was supersaturated and nanoparticles were precipitated. The influence of antisolvent flow rate (1.6, 2 and 2.4 mL/min), temperature (34,40 and 46), solute concentration (20,60 and 100 mg/mL) and pressure (9,12 and 15 MPa) on particle size and particle size distribution were studied. Particle analyses were performed by scanning electron microscopy (SEM) and Zetasizer Nano ZS. The mean particle size of 5-Fluorouracil was obtained in the range of 260-600 nm by varying the GAS effective parameters. The High performance liquid chromatography (HPLC) and Fourier transforms infrared spectroscopy (FTIR) analyses indicated that the 5-Fluorouracil nanoparticles were pure and the nature of the component did not change. The experimental results indicated that increasing the antisolvent flow rate and pressure, while decreasing the temperature and initial solute concentration, led to a decrease in 5-Fluorouracil particle size. (C) 2013 Elsevier B.V. All rights reserved.