Seven new pyrazole derivatives were designed, synthesized and tested for their in vivornantimalarial activity using the mice infected with P. berghei. All the synthesizedrncompounds were tested for their in vivo antimalarial activity at a dose of 20 mglkg. Fourrnof the most active compounds were tested at 40 mglkg. All of them except one had arnsignificant antimalarial activity. Among all the synthesized compounds, compound 2b (1-rn(4-chlorophenyl)-3-phenyl-l H-pyrazole-4-carbaldehyde), 3a (N'-Â«3-phenyl-l-p-tolyl-rn1 H -pyrazol-4-yl)methylene )isonicotinohydrazide), 2a (3-phenyl-l-p-tolyl-l H-pyrazole-rn4-carboxaldehyde) and 4b(1-Â«1-( 4-chlorophenyl)-3-phenyl-l H-pyrazol-4-yl)methylene)-rn2-(2,4dinitrophenyl)hydrazine) produced a mean percent suppression of 78.3%, 72.6%,rn67.2% and 61.9% respectively at 40mg/kg dose compared to the standard drugrnchloroquine which has produced 100% suppression. Compounds 2a, 2b, and 4b showedrnthe highest level of suppression at the first dose (20 mglkg), 73.0%, 67.4 and 65 .8%rnrespectively. Among the study compounds the ones that contain a free aldehydicrnfunctional group were more active than the corresponding hydrazone derivatives and thisrnfinding was supported by the docking result performed for three ofthe active compounds.rnIn addition, the acute toxicity study performed for the active compounds have shown thatrnthe LDso of these compounds were above 500 mglkg and hence safe to be used.rnKey words: pyrazole, P. berghei, in vivo, antimalarial activity