In this study, the particle emission characteristics of 10% alternative diesel fuel blends (Rapeseed Methyl Ester and Gas-to-Liquid) were investigated through the tests carried out on a light duty common-rail Euro 4 diesel engine. Under steady engine conditions, the study focused on particle number concentration and size distribution, to comply with the particle metrics of the European Emission Regulations (Regulation NO 715/2007, amended by 692/2008 and 595/2009). The non-volatile particle characteristics during the engine warming up were also investigated. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, can result in a noticeable reduction of the total particle numbers; however, the number of nucleation mode particles can increase in certain cases. For all the fuels tested, the increase of engine load results in a general reduction of particle numbers and an increase of particle mean diameters while increasing EGR leads to increased total particle numbers, which are mainly in the nucleation mode. The engine particle emissions suffer much higher numbers of the nucleation mode non-volatiles during warming up than during normal operations.