Malaria remains a public health problem in several areas of Banjamegara regency. Drug resistance or treatment failure is one of the main obstacles in controlling the disease in this area. To support The Malaria Control Program, since July 2001 up to June 2002 monitoring of the efficacy of chloroquine as a first line drug for uncomplicated falciparum malaria treatment was conducted using WHO's method version 2001 as guideline. The activities were conducted in two Health Centers (Banjarmangu I and Banjarmangu Il). It was found that only 37.21% (16/43) cases showed ACPR (Adequate Clinical and Parasitological Responses), 6.98% (3/43) cases with ETF (Early Treatment Failure) and 55.81% (24/43) cases considered as LTF (Late Treatment Failure). The over all treatment failure was 62.79% (27/43). The fever clearance time (FCT) in ACPR patients mostly (88.89%, 8/9) happened on day-I. Seven patients had no temperature increase since day-O (below 37.50 C). While the parasite clearance time (PCT) on day-2 was 43.75% and on day- 3 was 50%. It was concluded that chloroquine treatment for uncomplicated falciparum malaria in HCI area of Banjarnegara regency showed: (l), high proportion of treatment failure (62.79%) and high cumulative incidence of treatment failure within 28 days (62.60%) as well. (2) There was a proportion increase of treatment failure from 28.57% to 62.79%, during 1989 — 2002.