In a thermal recording medium including a basic chromogenic dye, a developer and a sensitizer, a composition for a thermal recording medium which composition contains 50 ppm to 5.0 mass % of 1-(3-methylphenoxy)-2-(4-methylphenoxy)ethane and/or 1,2-bis(4-methylphenoxy)ethane in 1,2-bis(3-methylphenoxy)ethane is used as said sensitizer, whereby the 1,2-bis(3-methylphenoxy)ethane compound is remarkably improved in milling property in the preparation of the above sensitizer, and a thermal recording medium is provided without impairing the colorability, etc., such as thermal colorability.