Ultrafine particles and NOx emissions of two kinds of biodiesels and their blends with diethyl ether (DEE) as an additive were compared under two engine speeds and three loads on a turbocharged, high-pressure, common rail diesel engine. A single spray injection and equivalence ratio distribution are used to explain the results. The study shows that biodiesel and biodiesel-DEE blend consume more fuels than diesel but slight variation in thermal efficiency. NOx emissions of waste cooking oil biodiesel are less than those of soybean biodiesel. At low and medium loads, DEE blending reduces the NOx emission. At all engine loads and speeds, the shape of ultrafine particle number distribution curve is unimodal, and fuel type slightly affects the shape of distribution curves. The number/mass distribution curves shift to fewer particles when operating on biodiesel and the curves further move to downward when DEE is added. Nanoparticles do not increase when operating on biodiesel or biodiesel-DEE blend. Total number concentration of ultrafine particle is decreased in biodiesel and it's further decreased in the presence of DEE. The equivalence ratio distributions of waste cooking oil biodiesel and its DEE blend are shrink compared with soybean biodiesel and its DEE blend, this could explain the reason for waste cooking oil biodiesel emits fewer particles than those of soybean biodiesel.