To effectively utilize waste paper and thereby obtain a reinforced rubber excellent in rupture properties by dissociating waste paper in advance in an aq. alkali soln., mixing the soln. with a rubber latex, and coagulating the latex.

Waste paper, pref. waste newspaper, is dissociated in advance in an aq. alkali soln. (e.g. a 5% aq. NaOH soln.), pref. at a pH of 9-10, e.g. with a pulper and then is mixed into a rubber latex, which is coagulated with an acid (e.g. hydrochloric acid) to give a reinforced rubber. The content of waste paper in the reinforced rubber is pref. 1-40 wt.% of the solid content of the latex. A natural rubber latex, an SBR latex, an NBR latex, a CR latex, a hydrogenated NBR latex, and a chlorosulfonated polyethylene latex are listed as the above-mentioned rubber latex.