New isatins based on Schiff bases were prepared from hydrazine, 5-substituted isatins, and aldehydes under reflux in ethanol. The structures of the synthesized compounds were elucidated by using IR, 13 C NMR, 1 H NMR spectroscopy and elemental analysis. All the compounds were tested in vitro antioxidant activity with free radical scavenging method using by 1,1-diphenyl-2-picryl hydrazyl (DPPH). The results were given with calculated IC50 values.