An improved process is provided for the bromination of isoolefin-conjugated diolefin polymers by brominating said polymer in solution in selected halogen-containing hydrocarbons as solvent. There is also provided an improved product of said process wherein the brominated polymer contains not less than 80 percent of the bound bromine atoms in a form suitable to participate in the vulcanization of the polymer and wherein not less than 70 percent of the bound conjugated diolefin units are similarly so brominated.