Malaria and leishmaniasis are the most prevalent tropical diseases caused by protozoan parasites.rnHalf of world's population is at risk of malaria and more than 2 million of new cases ofrnleishmaniasis occur annually. There are no effective vaccines available for these diseases andrncurrent treatments suffer from several limitations. Therefore, novel drugs for malaria andrnleishmaniasis are much-needed.rnIn this work, some derivatives of 2-styryl-4(3H)-quinazolinones have been synthesized usingrndifferent chemical reactions like cyclization, condensation and hydrolysis. The in vivo anti-rnmalarial activity of these compounds on P.berghei infected mice was found to be low tornmoderate with an oral dose of 0.04846 mmol/kg/day. The dose employed for the antimalarial testrnwas equivalent to 25 mg/kg of chloroquine phosphate which causes 100% inhibition of thernparasite.rnAmongrnthernsynthesizedrncompounds,4-{(1E)-2-[3,4-dihydro-3-(methylphenyl)-4-rnoxoquinazolin-2-yl]vinyl}-3- methoxyphenyl acetate IVc, showed better activity with percentrnsuppression of 47.44. The other test compounds IVa, IVb, IVd, and Va-Vc exhibitedrncomparable activities. On the other hand, the synthesized compounds were evaluated for their inrnvitro anti-leishmanial activity against L. donovani. Except for Compounds IVb and IVd whichrnhas IC50 value of 3.3248 and 3.3260 Î¼g/ml respectively, the test compounds such as IVa, IVcrnand Va-Vc (IC50 value 0f 0.0212-2.2654 Î¼g/ml) exhibited better potency than the reference drugrnmiltefosine (IC50 = 3.1911Î¼g/ml). In addition, compound IVa (IC50 = 0.0212 Î¼g/ml) displayedrnbetter antileishmanial activity than the reference drug amphotericine B (IC50= 0.0460Î¼g/ml).rnCompounds IVb-Vc showed less activity than the reference drug amphotericine B.rnKeywords: 2-styrylquinazolin-4(3H)-one, in vivo anti-malarial activity, in vitro anti-leishmanialrnactivity and acute toxicity