Measurements of the particle size distribution (PSD) provide important insight into the nature of particulate matter (PM) and its sources as stricter PM emission regulations (both mass & number based) are being implemented. A previous study by the authors suggested a link between the change in PSD shape and changing amounts of direct-injected fuel. In this study, the effect of direct-injected fuel on the PSDs from dual-fuel combustion strategies is investigated in greater depth. The PSD data were measured using a scanning mobility particle sizer (SMPS) and acquired in a light-duty single cylinder diesel engine operated using conventional diesel combustion (CDC) and two diesel/natural gas dual-fuel combustion strategies. Three different direct-injection (DI) fuels (diesel, 2,6,10-trimethyldodecane (farnesane), and a primary research fuel (PRF) blend) and two different injector nozzles were used in this study. The DI fuels were chosen to have similar energy and ignition characteristics (heat of combustion and cetane number) but different physical and chemical properties (volatility, aromatics %, viscosity, density). The two nozzles (with different orifice diameter and spray angle) allowed a wide range in DI fuel quantity for the dual-fuel combustion strategies. The results suggested that spray breakup and atomization process may have a strong impact on accumulation-mode particle concentration. The chemical properties of the DI fuel showed less impact on PSD shape and magnitude compared to physical properties. The DI fuel quantity was found to slightly affect the PSD magnitude in dual-fuel combustion strategies.