The effects of engine load and dilution conditions on the gas-particle partitioning of primary organic aerosol (POA) emitted from a light-duty diesel engine were investigated in a constant volume container (CVC). A new method was adopted to determine the POA concentration by using the combination of an OC/EC analyzer and a scanning mobility particle sizer (SMPS). A thermodenuder (TD) combined with a gas-chromatography/mass-spectrometry (GC/MS) was further used to study the temperature effect on the POA phase partitioning. Our results indicate that the engine load significantly affects the total organic carbon (OC) emissions while the dilution ratio (DR) influences the phase partitioning. Both sorption and evaporation are observed during the isothermal dilution process. Phase partitioning of the organic aerosol (OA) is dominated by sorption at low dilution condition and by evaporation of the adsorbed/ absorbed OA at high dilution condition. A further analysis on the TD experimental data obtained at different engine loads suggests that the OA from the medium load is more sensitive to the temperature while the OA from the high load is hard to evaporate. Two TD kinetic models based on volatility distribution are evaluated and the results are compared with the experimental data. The present study demonstrates the importance of dilution conditions and engine loads on the phase partitioning of diesel POA emitted from light-duty diesel engines at the near tailpipe environment.