New pyrazole-based thiazolyl hydrazone derivatives were obtained via the ring closure reaction of 3,5-dimethyl-1H-1-phenylpyrazole-4-carboxaldehyde thiosemicarbazone with 2-bromoacetophenone derivatives. The compounds were investigated for their cytotoxic effects on A549 and NIH3T3 cell lines. Among these compounds, compound 2i bearing a trifluoromethyl substituent can be identified as the most promising anticancer agent against A549 cancer cell lines. Compound 2i exhibited its inhibitory effect on A549 cells with an IC50 value of 0.0316 mM, whereas cisplatin showed its anticancer activity with an IC50 value of 0.01 mM. According to the IC50 values, the inhibitory effect of compound 2i on A549 cells can be considered to be selective when compared with its effect on NIH3T3 cells.