Abstract: Plasmodium falciparum(Lab.culture FCR3 isolate) developed resistance to sodium artesunate after exposure to the drug in vitro.The drug effective concentration which resulted in 50 per cent schizont maturation inhibition (IC50) was 1.6ng/ml (4.1nmol/L) before exposure to the drug.After 130 days of discontiguous exposure to sodium artesunate in a stepwise fashion,the sensitivity of the isolate to the drug decreased,with its IC50 3-fold higher than that of the parent isolate.The resistance to artesunate decreased significantly after the resistant line was grown in drug-free medium.