14C-Propoxur (Baygon®) was synthesized through the reaction of o-isopropoxyphenol with methyl isocyanate –14C. The product was isolated chromatographically on Florisil and crystallized from carbon tetrachloride. The purity and structure were confirmed using infrared spectra, melting point, co-chromatography on Florisil column, and silica-gel G thin layer chromatography. The purity was found to be at least 99%. The rate of absorption and other characteristics of14C-propoxur resistance inAnopheles Stephensi from the south coast ot Iran was investigated. The mortality of strain adults was 100% after a one hour exposure when 1 ppm14C-propoxur was used. Moreover, the mortality was not changed when a lower concentration (5 ppm) was used. On the other hand, the absorbance of14C-propoxur in several strains ofA. Stephensi has been determined. The identity and TLC characteristics of products formed after 1 and 2 hours exposure, respectively, to14C-propoxur have also been investigated.