A novel series of substituted pyrazolopyrimidine derivatives have been synthesized from substituted hydrazine derivatives and ethoxy (methylene) malanonitrile gives an intermediate (5-amino-1- substituted phenyl pyrazole-4-carbonitrile) (1) which on further react with formic acid, acetic acid/HCl and formamide gives series of (1- substitutedphenyl)1H pyrazole [3,4-d] pyrimidine-4(5H)-one (2). The synthesized compounds were characterized on the basis of IR, 1H NMR and Mass spectral data. Furthermore, these newly synthesized compounds were screened for their antioxidant activity by DPPH free radical scavenging method. Unfortunately none of the compound shows antioxidant activity.