A synthetic polyisoprene rubber latex produced by emulsifying a solution of polyisoprene rubber in an organic solvent with water and removing the solvent from the resulting oil-in-water emulsion is significantly improved with respect to mechanical stability, wet gel strength and dry film strength by utilizing, as a polyisoprene rubber, a modified polyisoprene rubber prepared by introducing from about 0.03 to 20 carboxyl groups per 100 recurring units of isoprene monomer present in the synthetic cis-1,4-polyisoprene rubber.