The objective of this work is to investigate the influence of waste cooking oil biodiesel on oxidation reactivity and nanostructure of particulate matter (PM). The test was carried out in a small agricultural diesel engine. PM samples were collected by MOUDI and subjected to TGA, Raman, NEXAFS and TEM. According to TGA, when waste cooking oil biodiesel quantity increases in the fuel, PM shows a higher volatile organic fraction (VOF). When the blend ratio of biodiesel increases to 50%, lower ignition temperature and burnout temperature are observed, signifying higher oxidation reactivity. Raman spectroscopy shows a higher graphitic-like structure and a lower polyene-like structure for pure biodiesel compared to pure diesel. With the addition of biodiesel, the crystallite dimension of PM increases. C(1s) NEXAFS spectra shows that there are many types of functional groups on the surface of PM. Pure biodiesel PM has lower phenolic, aromatic C-OH and ketone C=O groups than pure diesel and biodiesel/diesel blend PM samples. The analysis of TEM indicates the morphology of PM samples looks like chain shape. The primary particle coheres more closely and the average size of primary particles exhibits a decrease with the increase in biodiesel blend ratios. (C) 2016 Elsevier Ltd. All rights reserved.