Inorganic salts are generated in the production process of metal salts, such as sulfonates, sulfates and phosphates. When such metal salts containing inorganic salts are added as an antistatic agent to a polymer for producing polyurethane fiber, the inorganic salts cause fiber breakage or pack choking in fiber extrusion process. In addition, such antistatic agents are highly hygroscopic and contain trace of water. When such an antistatic agent is added to the material for polymerizing polyurethane, the alcohol and water in the agent react with isocyanate to result in lowered degree of polymerization and generation of oligomer. Such polyurethane polymer is spun into fiber of low elongation and tenacity. The material for polyurethane elastic fibers of the present invention comprises a mixture of 5 to 95 weight percent of at least one of the above-mentioned antistatic agents and 95 to 5 weight percent of a isocyanate-free starting material for elastic fibers, and eliminates the above troubles.