PROBLEM TO BE SOLVED: To provide a method for producing a skim rubber by using a serum of a deproteinized natural rubber latex. SOLUTION: A proteolytic enzyme and a surfactant are formulated with a natural rubber latex to carry out the proteolytic treatment, and the product is subjected to a concentration treatment to provide the serum of the deproteinized natural rubber latex, and at least one kind selected from a group comprising an amine salt-type cationic surfactant, a dialkyl quarternary ammonium salt-type cationic surfactant and imidazolinium salt-type cationic surfactant is added to the obtained serum to provide the objective skim rubber. The amount of the formulated cationic surfactant is preferably >=0.1 g based on 100 g of the liquid.