The purpose of this study was to investigate the functional properties of medicinal plant extracts. Four kinds of medicinal plants, Dioscorea batatas(DB), Armeniacae Semen(AS) Crataegus pinnatifida Bunge(CP) and Ponciri Fractus(PF), were extracted with water and 70% ethanol and the extracts were tested for their electron donating ability(EDA), nitrite scavenging ability(NSA) and inhibitory effects on cancer cells(MDA cell and A549 cell)growth. EDA at 100-1,000 ppm of water extract ranged from 3% to 14%, 14% to 36%, 29% to 72% and 14% to 43%, and that of ethanol extract ranged from 9% to 62%, 27% to 59%, 33% to 89% and 14% to 44%, in DB, AS, CP and PF, respectively. NSA of extracts measured at various pH(1.2, 3.0, 4.2, 6.0) showed the highest ability in all extracts at pH 1.2 and decreased with increasing pH. The highest NSA of water extracts of 1,000 ppm at pH 1.2 was 6%, 31%, 55% and 44% and that of ethanol extract was15%, 32%, 69% and 52%, in DB, AS, CP and PF, respectively Inhibition ratio of water and ethanol extracts on MDA cell growth was 24% and 17%, 51% and 93%, 46% and 69%, and 48% and 47%, while that on A549 cell was 18% and 9%, 6% and 3%, 7% and 3%, and 43% and 11%, at 1,000 ppm, in DB, AS, CP and PF, respectively.