Tehran is located in a valley at the foot of the Alborz Mountains in northern Iran (35 degrees latitude north). Urban expansion in Tehran resulted from a high rate of population growth and rural-urban migration combined with a strong tradition of centralization in the capital. Airborne particulate of Tehran's atmosphere was fractionated in a 6-stage high-volume cascade Impactor. The first objective was to measurement of PM in twenty sites in Tehran areas. Other objectives were to obtain detailed measurements of aerosol size distribution in Tehran's atmosphere during the 2004 at five sites. In all samples the PM is high for stage 6 (< 0.49 Î¼m). In Enghelab station mean of PM value (< 0.49 Î¼) is 260.97 Î¼g/m3. The highest PM (10-7 Î¼m) concentration is found 115.12 Î¼g/m3 at the Enghelab station. And the highest PM (3-1.5 Î¼m) was found 40.5Î¼g/m3 at the Baseej site.