Abstract: Forty-five condensation products of furan-, pyrrole-, and Nmethyl pyrrole-α-carboaldehyde with N⁴-3-or 4-substituted phenyl semicarbazides and thiosemicarbazides were designed and synthesized to optimize the antiulcer activity. Quantitative Structure-activity relationships reveal that in the series of semicarbazones increase in hydrophobicity of molecules and introduction of electron-repelling groups onto the phenyl ring raise the antiulcer activity; Generally, the activity of semicarbazones is higher than that of the corresponding thiosemicarbazones. The large spans between activity and toxicity of compounds No.17 and 30 led to further investigation of pharmacological actions.