Speed and load of diesel engine vehicles are the important factors affected on the fine particulate matter emission in Thailand.<strong> </strong>This study aimed to study the relation of speed and load of diesel engine vehicles affected on the emission of fine particulate matter in Thailand and also related to the emission of the exhaust from diesel engine vehicles. The experiment was designed into a x b Factorial Experiment in Completely Randomized Design. It was divided into 2 experiments as follows: 1) to study the emission of fine particulate matter in Euro 4 diesel engine vehicles, and 2) to study the emission of fine particulate matter in Euro 3 diesel engine vehicles. Moreover, it was to study 3 levels of speed in the driving form of diesel engine vehicles under Bangkok Driving Cycle, 3 levels of load, and 3 replications by using the experiment in Chassis Dynamometer System, and demonstrating the driving similarly to the actual driving. The samples of fine particulate matter from the exhaust were from the speed and load by using Micro-Orifice Uniform Deposition Impactors; MOUDI which had the size from 0.056-18 microns with the flow rate at 30 liter/ minute. The result from this study was found that the experiment of Euro 4 diesel engine vehicles had the factors of speed and load which affected on the emission of fine particulate matter at the level of 0.05, and F-value was 240.03 and 4.60 respectively. About the experiment of Euro 4 diesel engine vehicles, it had the factors of speed and load which affected on the emission of fine particulate matter at the level of 0.05, and F- value was 796.92 and 18.46 respectively. At the speed of 7.8 km/hr, the loads of empty vehicle and 1,000 kg of Euro 3 diesel engine vehicles were different at the level of 0.05. While the speed of 7.8 km/hr was at empty vehicle and 1,000 kg of Euro 4 diesel engine vehicles, it was not different in statistical significance. Therefore, there should be the regulations to control the load of the Euro 4 diesel engine vehicles lower than standard in the city with high traffic jam.