An experiment in a diesel engine fueled with diesel /ethanol blends was conducted,and the particle concentration and particle size distribution of the particulate matter from the diesel engine were investigated by DMS500 analyzer with fast response particulate.Then,the size distribution,mass concentration and geometric mean diameter of the particulate matter obtained under different running conditions of engine with different ethanol ratios were analyzed.The results show that ( 1) the particulate matter from diesel /ethanol blends follows a logarithmic distribution,which has two modes,namely,nucleation mode and accumulation mode; ( 2) with the increase of ethanol ratios,the nucleation mode particle number ( PN) density significantly decreases under a low load,while under medium and high loads,the accumulation mode PN density significantly decreases with an increase of the nucleation mode particle ratio and a decrease of the particle size; ( 3) for the particulate matter from diesel /ethanol blends,the mass concentration is lower than that from diesel,and the particle mass concentrates mostly in the accumulation mode; and ( 4) after the addition of ethanol to diesel,the geometric mean diameter of particulate matter significantly decreases,and it decreases gradually with the increase of ethanol ratios.