New sydnone derivatives bearing a substituted phenyl ring at the 3-position have been synthesized. Two separate series of 3-(carboxyphenyl)sydnone derivatives have been prepared by cyclization of the corresponding N-nitroso-N-(carboxyphenyl)-glycine 3. The obtained 3-(carboxyphenyl)sydnones 4 were subjected to a series of different chemical reactions on the carboxylic acid group. Compound 5, the potassium salt of 4a, was reacted with alpha-chloroacetanilide derivatives 6 to give the corresponding esters 7. On the other hand, the acid hydrazide 9 was condensed with different aromatic aldehydes to give the corresponding arylidene derivatives 10. The synthesized compounds were tested for their antibacterial activities against both gram-positive and gram-negative organisms. Some of the test compounds exhibited high activity; among them, 10d is considered to be a lead compound possessing high broad-spectrum antibacterial activity.