This paper reports a synthetic study in the condensation of ethyl alkoxy-alkylmalopates with urea, thiourea, and guanidine. Ethyl alkoxymalonates (Ⅵ,R=n-C₃H₇,n-C₄H₉,n-C₄H₉,i-C₅H₁₁ and C₆H₅CH₂) were pre-pared from the corresponding ethyl alkoxyacetates by ethoxalylation with subsequent pyrolytic decarbonylation. Various Ⅵ were then alkylated by standard method to give homologous ethyl alkoxy-alkylmalonates (Ⅶ,R'=CH₃,C₂H₅,n-C₃H₇ and n-C₄H-9). The ease with which ethyl alkoxy-alkylmalonates (Ⅶ) condense with urea, thiourea, and guanidine under the standard conditions promoted by sodium ethoxide varies considerably. All but one ethyl alkoxy-alhlmalonate (Ⅶ,R=n-C₆H₅CH₂;R'=CH₃,C₂H₅,n-C₂H₅) which gave a low yield of 5-alkoxy-5-alkylbarbituric acid (Ⅰ, Y=O) failed to react with urea.