Mixed crude palm oil(MCPO),the mixture of palm fiber oil and palm kernel oil,has become of great interest as a renewable energy source.It can be easily extracted from whole dried palm fruits.In the present work,the degummed,deacidified MCPO was blended in petroleum diesel at portions of 30% and 40% by volume and then tested in agricultural diesel engines for long term usage.The particulates from the exhaust of the engines were collected every 500 hr using a four-stage cascade air sampler.The 50% cut-off aerodynamic diameters for the first three stages were 10,2.5 and 1μm,while the last stage collected all particles smaller than 1μm.Sixteen particle bounded polycyclic aromatic hydrocarbons(PAHs) were analyzed using a high performance liquid chromatography.The results indicated that the size distribution of particulate matter was in the accumulation mode and the pattern of total PAHs associated with fine-particles(< 1μm) showed a dominance of larger molecular weight PAHs(4-6 aromatic rings),especially pyrene.The mass median diameter,PM and total PAH concentrations decreased when increasing the palm oil content,but increased when the running hours of the engine were increased.In addition,Commercial petroleum diesel(PB0) gave the highest value of carcinogenic potency equivalent(BaP eq) for all particle size ranges.As the palm oil was increased,the BaP eq decreased gradually.Therefore the degummed-deacidified MCPO blends are recommended for diesel substitute. Mixed crude palm oil (MCPO), the mixture of palm fiber oil and palm kernel oil, has become great interest as a renewable energy source. It can be easily extracted from whole dried palm fruits. In the present work, the degummed, deacidified MCPO was blended in petroleum diesel at portions of 30% and 40% by volume and then tested in agricultural diesel engines for long term usage. The particulates from the exhaust of the engines were collected every 500 hr using a four-stage cascade air sampler. The 50% cut-off aerodynamic diameters for the first three stages were 10, 2.5 and 1 μm, while the last stage collected all particles smaller than 1 μm. Sixteen particles bounded polycyclic aromatic hydrocarbons (PAHs) were analyzed using a high performance liquid chromatography. results indicated that the size distribution of particulate matter was in the accumulation mode and the pattern of total PAHs associated with fine-particles (<1 μm) showed a dominance of larger molecular weight PAHs (4-6 aromatic especially pyrene. The mass median diameter, PM and total PAH concentrations decreased when increasing palm oil content, but increased when the running hours of the engine were increased. In addition, commercial petroleum diesel (PB0) gave the highest value of carcinogenic potency equivalent (BaP eq) for all particle size ranges.As the palm oil was increased, the BaP eq decreasing gradually. ago the degummed-deacidified MCPO blends are recommended for diesel substitute.