Diesel blended with minor biodiesel has been implemented as an initial act on alternative energy issue worldwide. Biodiesel brings the change of pollutant emissions after a burning process. The surface morphology and biotoxicity comparisons of particulate emitted from diesel and biodiesel blend was carried out using an unmodified four-stroke engine generator. Particulate size distribution was measured using a micro-orifice uniform deposit impactor. The Microtox test and the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay indicate the acute and cell viability, respectively, for the particulate collected in the engine exhaust gas. The results showed that diesel produces more particulate than biodiesel blend as expected, and the light operating load does not favor a particulate reduction. No significant trend was observed between the acute toxicity and engine operating load. The engine optimum operation differed fueling with diesel and B10. Additionally, engine running at a high operating load was observed to reduce the particulate cytotoxicity in the engine exhaust.