Aqueous ring opening metathesis polymerizations of the monomer exo, exo-7-oxabicyclo [2.2.1] hept-5-ene-2,3-dicarboxylic acid with RuCl₃ and K₂[RuCl₅H₂O] were studied by gravimetric and ¹³C NMR techniques to gain an additional insight into the initial stages of the reactions. The studies showed that the conversion of monomer to polymer is dependent on the reaction time, as well as the type of the Ru starting compound, with occurrence of an induction period. The ruthenium content in the isolated polymers is less than 30% from the initial amount.