The present work focused on the effect of injection timing, which changed from 23 degrees CA before top dead center (-23 degrees CA ATDC) to 8 degrees CA after top dead center (8 degrees CA ATDC), on particle size distribution (PSD) from a diesel engine operated under 0% and 40% EGR rates. The results show that PSDs under 0% EGR is dominated by the nucleation mode (NM), and injection timing shows no significant effect on NM on a log plot, while the early and late injections produce the low AM. Under 40% EGR, PSD is dominated by NM with very early and late injections, while it is dominated by the accumulation mode (AM) for -20 to -5 degrees CA ATDC, and an apparent "AM bump" occurs at round -10 degrees CA ATDC. The phenomenon of "AM bump" indicates that the coupling early or late injection and EGR favors low temperature combustion (LTC), and which results in a simultaneous reduction in soot (AM) and NOx emissions. A negative relationship between N-nuc and N-acc with the change in injection timing suggests that LTC potentially promotes the formation of NM. A more evident trade-off relationship between N-tot and M-tot is presented under 40% EGR than that under 0% EGR, which indicates that in-cylinder PM formation and oxidation is more dependent on injection timing under 40% EGR. (C) 2014 Elsevier Ltd. All rights reserved.