PURPOSE: A trimellitic ester, consisting of a trialkyl trimellitate and trimellitic ester polymer, and useful as a plasticizer for thermoplastic resins, solvents or diluents for coating materials, etc.

CONSTITUTION: A trimetllitic ester consisting of 60W20wt% trialkyl trimellitate, e.g. trimethyl trimellitate, and 40W80wt% polymer of the formula[R is 1W18C alkyl; X is 1W20C methylene or polymethylene which may have ethereal bonds in the backbone thereof; (n) is an integer 1W10]. The ester has good compatibility with thermoplastic resins, particularly vinyl chloride or vinylidene chloride resin, and is usable together with a lead stabilizer. A thermoplastic resin composition plasticized with the ester will not transfer the ester even on contact with ABS resin, etc. and has improved resistance to heat, oil and staining.