This article proposes the first report on the synthesis of nanometric crosslinked polynorbornene particles by ring-opening metathesis polymerization in dispersion using ruthenium-based complex (PCy3)2Cl2Ru?CHPh as initiator. Stable but raspberry-shaped particles were obtained. In this study, a particular attention was paid to the influence of the crosslinker nature and addition mode on reaction kinetics and morphology of the latex particles. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012