The hydroxyl group content in 1-chlorobutadiene–butadiene rubber (CB–BR) was increased by the following two methods: (1) heating of the CB–BR latex to hydrolyze the unstable chlorine in CB–BR and (2) introduction of hydroxyl by the Menschutkin-type reaction between 2-dimethylaminoethanol (DMAE) and the chlorine in CB–BR. By heating the latex at 70°C for 12 hr, 55% chlorine was hydrolyzed to result in a marked increase in hydroxyl group content in CB–BR, i.e., at least 55% chlorine is situated in the CB units of the 1,4-configuration. Heat-treated CB–BR was found to contain a small amount of conjugated triene structure by UV spectroscopy, which indicates that elimination of some unstable chlorine as hydrogen chloride occurs during latex heating. By reaction with DMAE, 44% chlorine was converted into hydroxyl in toluene at 27°C. CB–BR compounded with DMAE does not suffer from gelation by milling on an open roll. Thus, by these methods, high molecular weight butadiene rubber having various concentrations of hydroxyl groups is obtained.