Airborne particulate matter is an important factor in the quality of an indoor environment. In this study, a miniaturized particle sensor was developed to detect submicron-sized aerosols based on number counting. This particle number (PN) sensor was designed and fabricated for real-time measurement of total aerosol number concentration and geometric mean diameter. The sensor (hereafter called as PN1 sensor) comprised a particle-classification unit, a particle-charging unit, and a particle-detection unit. After integrating all the three units, the total number concentration and the geometric mean diameter of test aerosol particles were determined and the results were compared with those obtained using commercial instruments. First, the PN1 sensor was compared with a condensation particle counter (CPC) in lab-test. For this, different groups of monodisperse sodium chloride particles between 20 and 700 nm in diameter were used. Then the PN1 sensor was compared with a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). For this, the PN1 sensor data were obtained by varying the combination of two corona voltage and test particles (sodium chloride and polystyrene latex) size distribution. In addition to lab-test, field test was carried out with indoor aerosols in different places. The number concentration and geometric mean diameter of indoor aerosols were measured by PN1 sensor and compared with SMPS data. The number concentration was also compared with the results of CPC and Pegasor AQ Indoor (Pegasor, Finland) measurements.