In Jakarta, the main pollution sources are vehicles and industry, with motorized traffic accounting for 71% of the oxides of nitrogen (NOX), 15% of sulphur-dioxide (SO2), and 70% of particulate matter (PM 10 ) of the total emission load. Both urban population size and the fraction of the population that owns a pri-vate vehicle are increasing. The study objective is to determine the numbers of ultrafine particulate matter with an aerodynamic diameter of 0.1 mm or less, or PM0.1 inhaled by elementary school children, commute workers with private car and commute workers with public transport. A cross-sectional study design is implemented in Jakarta 2005. Ten elementary school children, ten commuters with private car and ten commuters with public transports are purpo-sively selected as subjects and measured personally for 3 x 24 hours using Condensation Particle Counter (CPC) real-time personal exposure measurement (measured in terms of the number of particles per cubic centimeter, or # cm-3). The average concentration of ultrafine particulate matter of elementary school children at home, on the road and at school is 29,254/cm3, 147,897/cm3 and 61,033/cm3 respectively. For those commuters with private car at home, on the road and at office is 29,213/cm3, 310,179/cm3 and 42,496/cm3 respectively. For those commuters with public transport, the concentration average of at home, on the road and at office is found higher: 35,332/cm3, 453,547/cm3, and 69,867/cm3, respectively.