An on-board PN analyzer (OBS-ONE-PN) has been developed to measure the engine exhaust solid particle in real-driving condition. The OBS-ONE-PN is designed based on the recommendation in the PN-PEMS draft proposal. The OBS-ONE-PN consists of heated sampling line, heated 1st dilution system, evaporation tube (catalytic stripper, CS), 2nd dilution system and particle detector. The volatile particulate matter emitted from automobile engine is removed by CS, and then the solid particles is counted in number concentration (particles/cm3) by a condensation particle count (CPC) method. The detailed specifications relating the OBS-ONE PN performance such as dilution factor accuracy, volatile particle removal efficiency, overall detection efficiency and durability test results are described in the manuscript. The OBS-ONE-PN is used to characterize PN emission from a gasoline and a diesel vehicle equipped a diesel particulate filter (DPF) device. Two test cycles, New European Driving Cycle (NEDC) and Worldwide harmonized Light duty Test Cycle (WLTC), were conducted in chassis dynamometer test bench. In order to obtain the correlation with PMP system, the solid particle counting system (SPCS, Horiba Ltd.) was employed during two test cycles. Furthermore, the OBS-ONE-PN was used to determine the PN emission behavior in the real-driving condition. The result of correlation analysis using the simple linear regression model showed a good correlationship between PMP system and OBS-ONE-PN. More finding relating the result of test cycles and the PN emission behavior during the real-driving condition will be discussed.