The effect of direct-injected fuel on particle size distributions (PSDs) of particulate matter emitted from dual-fuel combustion strategies was investigated. The PSD data were acquired from 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, and a primary reference fuel blend) and two different injector nozzles were studied. 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 suggest that the physical and chemical properties of the DI fuel may have a strong impact on PSD distribution shape and accumulation-mode particle concentration for CDC and natural gas combustion with a diesel-pilot-injection strategy. For diesel/natural gas RCCI combustion the PSD was found to be insensitive to the DI fuel when using two-stage dilution with a volatile particle remover. The DI fuel quantity was found to slightly affect the PSD magnitude for dual-fuel combustion strategies.