In this work, some derivatives of 2-pyrazolyl-4(3H)-quinazolinones have been synthesized byrncyclization and condensation reactions. The synthesized compounds were obtained in a goodrnyield (55.9-94%). The chemical structures of the final compounds were also verified byrnspectroscopic tools (IR, 1H NMR and elemental microanalyses). The in vivo anti-malarialrnactivity of these compounds against P.berghei infected mice was found to be moderate at oralrndose of 48.46 Î¼mol/kg/day. This dose is equivalent to 25 mg/kg of chloroquine phosphate whichrncauses 100% inhibition of the parasite. Among the synthesized compounds, 2-(3-(thiophen-2-yl)-rn4,5-dihydro-1H-pyrazol-5-yl)-3-phenylquinazolin-4(3H)-one, Xa, showed better activity withrnpercent suppression of 65.89. The synthesized compounds were also evaluated for their in vitrornanti-leishmanial activity against L. donovani. Among the synthesized compounds, compoundrnIXe (IC50=0.0121 Î¼g/ml) was found to possess four fold the potency of amphotericine Brn(IC50=0.0460 Î¼g/ml) while it was two hundred sixty four (264) times more potent thanrnmiltefosine (IC50=3.1911 Î¼g/ml). Compound Xa (IC50=0.0211 Î¼g/ml) was twice more potentrnthan amphotericine B and this is the second most active compound as anti-leishmanial agentrnamong the synthesized compounds. The synthesized compounds exhibited better inhibitoryrnactivity as indicated by their lower IC50 than miltefosine, except for compound XI. CompoundrnXI showed the least activity which might be due to the presence of a phenyl group on thernpyrazole N1. Furthermore, in the thiophen series cyclization of Î±,Î²-unsaturated compounds to therncorresponding pyrazoline analogs led to improvement in activity while the phenyl series showedrnconflicting results.rnKeywords: 2-pyrazolyl-quinazolin-4(3H)-one, in vivo anti-malarial activity, in vitro anti-rnleishmanial activity and acute toxicity.