To obtain a thermosetting polymer exhibiting excellent heat resistance, electrical characteristics, such as a low dielectric constant, and low water absorption, which are necessitated as electric and electronic materials, and useful as wiring base materials, etc., by subjecting a specific phenol and a diethynyl compound to oxidative coupling.

This thermosetting polymer is obtained by subjecting (A) 70-95 mol% of 2,6-diphenylphenol expressed by the formula and (B) 5-30 mol% of a diethynyl compound expressed by the formula: CH≡C-Ar-C≡CH (Ar is a divalent aromatic unit) (for example, m-diethynylbenzene) to oxidative coupling polymerization at 40-110°C, and has a weight-average molecular weight of 2,000-500,000 when measured by gel permeation chromatography. The component B is added, for example, in an amount of 5-30% based on the total amount of the component A and component B. The polymerization is preferably performed in the presence of a copper compound/amine-based catalyst in a solvent, such as toluene.