Polynorbornene latexes were prepared by ring-opening metathesis polymerization of norbornene (NB) in water carried out in miniemulsion. The ability of both lipophilic or hydrophilic initiators to polymerize NB under miniemulsion conditions has been investigated. With an oil-soluble initiator ((Cy3P)(2)Cl2Ru=CHPh) the miniemulsion polymerization of NB resulted in the formation of large and poorly stabilized particles that eventually coagulated. On the contrary, with a water-soluble initiator based on RuCl3 and an alcohol stable particles could be obtained as a result of the miniemulsion polymerization of NB. For each miniemulsion polymerization the role played by ionic and steric stabilizers such as sodium dodecyl sulfate and poly(styrene-b-ethylene oxide), respectively, on both the course of polymerization in miniemulsion and the particle stabilization has been investigated in detail.