Abstract: ObjectiveTo observe the effect of artesunate plus chloroquine for treatment of chloroquine-failed cases.MethodsThe 282 day in vivo method recommended by WHO for effect test of antimalarial drugs in middle and low endemic area of malaria was applied in the observation.ResultsIt was found that the treatment failure of the combination of these two drugs was 25% among the 44 cases.The resistance rate of RⅠ-RⅢ was 22.73%.Treatment failure was related to the response of parasite to antimalarial drugs,but not related to the parasite density on day 0.ConclusionThe combination was effective for the treatment of chloroquine-failed cases.If single regiment of chloroquine was regarded as the first line drug and the combination as the second line drug,the treatment failure probability of these two line drugs was only 11.66%.This two-line combination can be used in the field with low income of local patients when the medical emergency service was reachable.