Polynorbornene-based latex particles were prepared via dispersion ring-opening metathesis polymerization (ROMP) of norbornene (NB) in dichloromethane/ethanol medium and in the presence of a alpha-norbornenyl poly(ethylene oxide) macromonomer (NB-PEO). Colloidal dispersions in the 200=600 nm size range were obtained and characterized by electron microscopy and dynamic light scattering. This paper also investigates the reaction parameters that influence both the structure of the PNB-g-PEO graft copolymer formed and the characteristics of the resulting latex. In particular, the effect due to the macromoriomer-its structure, concentration, and molar mass-and also the role respectively played by the medium polarity, the monomer concentrations, and initiator concentrations are discussed. The mode of addition of norbornene was also investigated. Attempts to synthesize pure polynorbornene latex particles are also described using either unreactive PEO-based stabilizers or PNB-g-PEO seeds.