Disclosed are a method for manufacturing an outsole for shoes without applying an external mold release agent or mold lubricant onto a mold, and a formulating composition used at manufacturing a rubber outsole. One composition of an internal mold lubricant for manufacturing an outsole for use in footwears is consisting of highly branched hydrocarbon having molecular weight of 400 to 2800, carboxylic acid, metal salts of carboxylic acids, and phospholipids containing heat stable lecithin, Another composition of an internal mold lubricant for manufacturing an outsole for Use in footwears Is consisting of branched hydrocarbon having molecular weight of 800 to 2000, carboxylic acid, long chain carboxylic acids having molecular weight of 200 to 800, metal complex of rang chain carboxylic acids having molecular weight of 200 to 800, and ionomer.