Background: Frequency of tropical infection in Indonesia are still high nowadays. This condition can cause high frequency of antibiotic usage and antibiotic resistance in the future. Aim of this study was to quantify the antibiotic usage in tropical infection patients in Cipto Mangunkusumo Hospital on June 2014-June 2015 using defined daily dose (DDD) method. The advantage of this method is easy to apply, used to compare between different medicine with same therapeutic group, have similar efficacy but different dose requirement, and also compare between institution or area. Methods: It was a descriptive, cross-sectional study, used medical record as data sources. All tropical infection patients in Internal Medicine Ward, on June 2014-June 2015 period, were included in our study. DDD formula is DDD/100 bed-days= (total amount of antibiotic in gram/DDD value from WHO) x (100 / length of stay of all patients with tropical infection diseases). One DDD mean average maintenance dose per day for a drug used for its main indication for adults. Results: We found 34 patients with tropical infection diagnosis and only 22 patients used antibiotic. The total length of stay for tropical infection patients was 314 days. Three antibiotics with highest DDD were ceftriaxone (54.46), levofloxacin (24.20) and meropenem (21.66). The highest DDD in typhoid fever subjects was ceftriaxone and in leptospirosis subjects were levofloxacin and meropenem. The antibiotic usage pattern could be difference between institutions or area, depends on the etiology and microbial resistance pattern. There were six patients with malaria and DHF treated with antibiotics, even though these diagnosis are not indication for antibiotic treatment. It might be due to bacterial infection as comorbid condition. Conclusions: Ceftriaxone, levofloxacin, and meropenem were antibiotics with the highest DDD unit. The usage of antibiotics for viral and parasite infection might be due to secondary infection.