PURPOSE: To attain the regenerative utilization of a waste urethane polymer, by using the thermal cracking substance of the urethane polymer as an oil-water separating agent.

CONSTITUTION: When alkali metal hydroxide or alkali metal alcholate and amino alcohol are added to a urethane polymer consisting of polyether polyol and polyisocyanate to thermally crack the same at a reaction temp. of 100W 200°C, a highly viscous liquid or a pasty substance is obtained. When this substance is added to a mixed liquid comprising water and an oil in an emulsified state or dispersed state alone or in combination with a known serfactant, water and the oil are rapidly separated. When 50ppm of the obtained oil-water separating agent is added to an emulsion obtained by stirring 50ml fuel oil C and 50ml water, 100% water separating rate is attained within 120min.