An on-board solid particle number (PN) analyzer (OBS-ONE-PN) has been developed to measure PN concentrations in engine exhaust under real-driving conditions. Specification of OBS-ONE-PN is based on the recommendation in PEMS-PN draft. OBS-ONE-PN consists of primary diluter, heated transfer tube, heated catalytic stripper (CS), secondary dilutor and particle detector. Volatile fractions which is emitted from the automobile engine are removed by CS, and then only solid particles are counted by a condensation particle counter (CPC). Finally, the system provides results in number concentration. The detailed specifications relating to the OBS-ONE-PN performance such as dilution factor accuracy, volatile particle removal efficiency, overall detection efficiency and durability test results are described in this paper The OBS-ONE-PN is used to characterize PN emission from a gasoline vehicle. Two test cycles, New European Driving Cycle (NEDC) and worldwide harmonized light-duty driving test cycle (WLTC) were performed on the chassis dynamometer. In order to obtain the correlation with the reference system, the solid particle counting system (SPCS, Horiba Ltd.) was employed during two test cycles. Furthermore, the OBS-ONE-PN was used to characterize the PN emission behavior in the real-driving condition. The results of correlation analysis using the simple linear regression model showed a good correlation between the reference system and the OBS-ONE-PN. Findings relating to the results of the test cycles and the PN emission behavior during the real-driving condition were shown.