The zinc(II) complexes of the amino acids Schiff bases had been synthesized by one-step solvent-free reaction with L-leucine or L-alanine, salicylaldehyde and zinc acetate as materials. The compositions and structures of the complexes had been characterized by EDTA titration, elemental analysis, IR spectrum, X-ray powder diffraction and TG-DSC analysis. The compositions of two complexes are [ZnL(H2O)]?nH2O (L = sal-ala, sal-leu). Infrared spectra and the thermal decomposition process of the complexes show the presence of coordination water molecules. The zinc ion is coordinated through the Schiff base ligands as terdentate with O, O and N donors from carboxylic, phenolic and imino groups, and O donors from water molecule respectively. The coordination numbers of zinc ion is four. Thermal decomposition of the complexes proceeds in several stages: dehydration, oxidation pyrolysis of the ligands, and the final residues are zinc oxide.