This work clarifies the structural characterization and antioxidant activity between aromatic and 3-arylsydnonyl substituted hydrazino-thiazoles by further synthesizing a series of aromatic ring-substituted hydrazino-thiazole derivatives 8a—h and 9a—h. Hydrazino-thiazole derivatives 8a—h and 9a—h were obtained by reacting aromatic or heterocyclic aromatic aldehyde thiosemicarbazones 7a—h with cyclization reagents ethyl 2-chloroacetoacetate (2a) and 2-bromoacetophenone (2b), respectively. The ORTEP drawings of compounds 8g, 8h and 9f provide strong evidence of the structure of aromatic thiazole derivatives 8a—h and 9a—h. Undoubtedly, the structure of compounds 3e—h and 4e—h synthesized by the reaction of 3-aryl-4-formylsydnone thiosemicarbazones 1e—h with cyclization reagents 2a and 2b in the previous work should have the thiazole moiety, and not the thiazoline moiety. Both the new thiazole derivatives 8a—h and 9a—h and the 3-arylsydnonyl-substituted derivatives 3e—h and 4e—h were investigated to determine their antioxidant activity by two tests that have been highly documented—the direct scavenging effect on a stable free 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and the inhibition of the 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical. Results of this study demonstrate that not only the thiazole ring and the aryl ring has the contribution to the antioxidant activities, the sydnone ring of 3-arylsydnonyl moiety also has its considerable contribution.