Recently, it was reported that the atmospheric pollution levels of nitrogen dioxide (NO2) and particulate matter (PM) are not decreasing despite the introduction of stricter vehicle emission regulations. The difference between conditions of the test cycles defined by the vehicle emission regulations and the real driving can contribute to the differences between expected and actual pollution levels. This has led to the introduction of in-use vehicle emission monitoring and regulations by means of a portable emission measurement system (PEMS). An optimized on-board PM analyzer was developed in this study. The on-board PM analyzer is a combination of a partial flow dilution system (PFDS) particulate sampler and a diffusion charger sensor (DCS) for real-time PM signals. The measuring technology and basic performance of the analyzer will be explained. Acceleration of the vehicle can cause uncertainty of flow measurement in the PM sampler. The influence of the vehicle acceleration was minimized by compensation for each flowmeter. Good correlation in emission measurement between the on-board PM analyzer and a stationary PFDS used for certification tests in the engine test cell was observed. The on-board PM analyzer was installed in light duty diesel vehicles equipped with or do not equipped with a diesel particulate filter. The applicability of the analyzer to the on-board measurement and PM emission behavior during the real driving condition will be discussed.