Abstract: Abstract: Low-speed vehicles have a very high contribution to air pollution in China due to their considerable numbers, especially in the fringe area of city. In China, the low-speed vehicles emissions greatly exceed those of trucks and passenger cars because of their lower emission limits. Emissions of CO, HC, NOx and PM by low-speed vehicles accounted for 0.5%, 4.1%, 7.3% and 4.8% of the total vehicle emissions in 2012 in China. In 2005, the China Ministry of Environmental Protection issued the first-phase and second-phase emission standard (standards GB19756-2005 and GB19757-2005, respectively). However, there were not many research-based data about the emission characteristics of low-speed vehicles. In this study, a Portable Emission Measurement System (PEMS), which is comprised of a regulated gaseous emission analyzer (SEMTECH-DS) and an electrical, low-pressure impactor (ELPI), was introduced to study the emission characteristics of low-speed vehicles in real road. Six low-speed vehicles were measured on national and rural roads using PEMS, which can measure CO, HC, NOx and PM emissions. The results indicated that vehicle speed had a very big impact on pollutant emissions on both national and rural roads. Emissions on rural roadways were much more variable than those on national roadways because of the variability in vehicle speed. The ratios of acceleration and deceleration modes were not very high both on national and rural roads (28.48% and 33.76%, respectively). The emission factor of four pollutants was highest in acceleration mode on both national and rural roads. The CO, HC, NOx and PM emission factors in acceleration mode were 1.86, 1.32, 1.57, 1.22 times those in cruise mode, respectively. The CO, HC, NOx and PM emission factors in acceleration mode were 2.30, 1.42, 3.09, 1.39 times those in deceleration mode, respectively. The size distributions of particles emitted from low-speed vehicles were similar on national and rural roads. The ratio of coarse mode particles was very low (0.15 % and 0.16%, respectively) of the total particle number concentration on national and rural roads. Comparing the number concentration of particles emitted on national and rural roads, the particle-number concentration on rural roads was higher 32.0% than that on the national roads. Especially for particles of diameter 0.32 μm, the number concentration was 62.2% higher than that on the national road, probably due to the poor combustion in the engine cylinders. This report could provide some reference for future emission control policies for low-speed vehicles.