Salicylic aldehyde-N(4)-(4-ethoxyanilinyl)thiosemicarbazone (H2L) was synthesized by condensation between salicylic aldehyde (SA) and N(4)-(4-ethoxyanilinyl)thiosemicarbazide (TSCZ) in presence of glacial acetic acid as a homogeneous catalyst in ethanol. As a result of analysis by the surface response based on Box - Hunter model with the confidence level of 95%, the expectable yield reached the highest point (around 68%) at 80oC for 10 minutes when approximately 1 mole of SA reacted to equivalently 1 mole of TSCZ. The structure of H2L was solved by IR, UV-Vis, 1H and 13C NMR, HSQC, HMBC and HRMS, which indicated that the thioketone is the predominant form of H2L in the solid phase. The UV-Vis data in variety of pH showed that H2L was assigned to be a diacid with pKa1 = 8.8 and pKa2 = 13.6.