An improved process for the preparation of tris(nonylphenyl) phosphite is described which includes the steps of combining at least a 4 weight percent excess of nonylphenol (preferably 8 weight percent excess) with PCl.sub.3 with agitation and heating sufficient to liberate HCl formed during the synthetic reaction as a by-product and removing the excess nonylphenol from the tris(nonylphenyl) phosphite by thin film distillation to reduce the residual chloride level to 90 ppm or less, an acid number of 0.1 or less and a nonylphenol content after stripping of 0.1 weight percent or less. The temperature of the reaction was from room temperature to 130.degree. C., and the temperature of the evaporator which removes the excess nonylphenol is from 100.degree. C. to 350.degree. C., preferably from 150.degree. C. to 250.degree. C., under a system vacuum of from 0.01 mm Hg to 5 mm Hg.