Abstract A new series of N ‐substituted pyrazoline derivatives 6a–g , 7a–g , 8a–g , and 9a–g was synthetized by reaction of hydrazine derivatives and chalcone–thiazole hybrids bearing nitrogen mustard 5a–g . The chalcones 5a–g were obtained by Claisen–Schmidt condensation of thiazole‐2‐nitrogen mustard 3 and selected acetophenones 4a–g . These new compounds 6/7/8/9a–g were screened for their antifungal activity against Cryptococcus neoformans , with IC 50 values of 3.9–7.8 µg/ml for the N ‐3,5‐dichlorophenyl pyrazolines 9e – g . Interestingly, those compounds show low cytotoxic effects toward erythrocytes (RBC). In addition, N ‐acetyl ( 6a,b ) and N ‐formyl pyrazolines ( 7a , 7b , 7c , and 7g ) showed inhibitory activity against methicillin‐susceptible Staphylococcus aureus , methicillin‐resistant S. aureus , and vancomycin‐intermediate S. aureus , with the most important minimum inhibitory concentration values ranging from 31.25 to 125 µg/ml. Regarding the antiprotozoal activity, thiazolyl‐pyrazolines 9g , 8f , and 7c display high activity against Plasmodium falciparum, Leishmania (V) panamensis , and Trypanosoma cruzi , with EC 50 values of 11.80, 6.46, and 4.98 μM, respectively, and with 7c being approximately 2.6‐fold more potent than benznidazole with a selectivity index of 1.61 on U‐937 human cells, showing promising potential as a novel antitrypanosomal agent.