A series of new thiazole-hydrazones 3a-3n were synthesized, characterized, and screened for their $h$MAO-A and $h$MAO-B inhibitory activity by an in vitro fluorometric method. Selectivity indexes (SIs) were expressed as IC$_{50}$ (MAO-A) / IC$_{50}$ (MAO-B). Compound 3f showed promising $h$MAO-A inhibition with an IC$_{50}$ value of 1.20 $\mu $M and displayed a very significant SI of 0.04 towards $h$MAO-A. The mechanism of $h$MAO-A inhibition was investigated by enzyme kinetics using Lineweaver--Burk graphics. Compound 3f was further screened for its cytotoxicity by using a healthy NIH/3T3 mouse embryonic fibroblast cell line (ATCC CRL1658) and was evaluated as nontoxic at its effective concentration against $h$MAO-A. The ADME prediction of the compounds revealed that they may have good pharmacokinetic profiles, which is necessary for drug candidates.