1. A method has been developed for the GLC determination of impurities in mmm-5P4E polyphenyl ethers obtained by various methods. The methods provide individual quantitative determination of 11 different impurities with a single sample injection. 2. The contents of impurities in various polyphenyl ether samples have been determined qualitatively and quantitatively, with an accuracy of 10% relative. The sensitivity of determination of bromine-containing impurities is not less than 0.01% of sample weight; that of hydroxyl-containing impurities is not less than 0.06%. 3. The method that has been developed may be applied for the determination of purity of polyphenyl ethers with up to six rings, or that of m-phenoxyphenol and m-phenoxyphenoxyphenol.