An increasing concern has been growing in the last years toward health effects due to Particulate Matter (PM) emissions. This triggered the widespread diffusion of Diesel Particulate Filters (DPFs), which equip almost every Diesel car and truck on the market, allowing to get large reduction (in the order of 95% and more) in terms of PM mass.However, PM health effects are believed to be more related to particle number rather than to particle mass. This gave rise in Europe to new regulations for passenger cars on total particle number, that will be introduced from EURO6 on. Engine/Exhaust-System assembly is therefore under investigation, to better understand the effectiveness of aftertreatment components toward particle number reduction, especially by varying engine and exhaust-system design/operating conditions, and to compare particle number emissions to particle mass emissions.Given the background, an experimental study on particle emissions of a FIAT 2.01 EURO5 passenger car Diesel engine coupled to a DOC-DPF system is proposed in this paper. Experimental data have been gathered at the engine test bench of the University of Rome Tor Vergata. Data have been acquired with regard to ECE-EUDC representative steady state engine operating points, to highlight correlations among specific engine operating conditions and upstream/downstream DPF particle number distribution and mass. Special attention has been devoted to the analysis of three different DPF materials and specifications toward particle emissions, both in terms of mass and number, during the transient loading and regeneration processes, as well as during steady state operating conditions after DPF pre-conditioning. Moreover, effects related to the variation of key engine operating parameters, such as EGR and pressure injection, have been analyzed.