In order to explore the anticancer and antimicrobial activity associated with the thiazolone framework, several new (Z)-2-((5-(3-fluorobenzylidene)-4-oxo-4,5-dihydrothiazol-2-yl)amino)carboxylic acid derivatives have been synthesized in water as a solvent. All synthesized compounds were evaluated for anticancer and antimicrobial activity in vitro. Amongst these, the 3-methylbutanoic and the 3- or 4-methylpentanoic acid derivatives, the 3-hydroxy-, the 3-(1H-imidazol-4-yl) and the 3-(4-hydroxyphenyl)propanoic acid derivatives and the succinic acid derivative showed high antibacterial and antifungal activity. The unsubstituted propanoic acid derivative exhibited significant antibacterial activity against B. subtilis and significant antifungal activity against fungal strains, i.e., A. flavus. The in vitro anticancer studies revealed that the 3-(hydroxy)-, the 3-(1H-imidazol-4yl)- and the 3-(4-hydroxyphenyl)propanoic acid, or the succinic acid derivatives are the most active compounds against MCF-7 and BT-474 human breast cancer cell lines.