Résumé/Abstract The gas chromatography (GC) method was applied for the analysis of reaction mixture from synthesis of2-carboethoxy-2, 5-diethyl-3, 4-dihydro-2H-pyran. Relative errors of GC determinations not exceeded more than 7-8%. The reaction optimal conditions were proposed on the basis of such criteria as the conversion of α-ethylacrolein, yields and selectivities of main products by using the GC method.