BACKGROUND/OBJECTIVES: Malnutrition during hospitalization is linked to increased morbidity and mortality, but there are insufficient studies observing clinical factors contributing to weight loss during hospitalization in Indonesia. This study was therefore undertaken to determine the rate of weight loss during hospitalization and the contributing factors. SUBJECTS/METHODS: This was a prospective study involving hospitalized adult patients aged 18–59 yrs, conducted between July and September 2019. Body weight measurement was taken at the time of admission and on the last day of hospitalization. The factors studied were malnutrition at admission (body mass index < 18.5 kg/m2 ), immobilization, depression (Beck Depression Inventory-II Indonesia), polypharmacy, inflammatory status (neutrophil-lymphocytes ratio;NLR), comorbidity status (Charlson Comorbidity Index; CCI), and length of stay. RESULTS: Totally, 55 patients were included in the final analysis, with a median age of 39 (18-59 yrs) yrs. Of these, 27% had malnutrition at admission, 31% had a CCI score > 2, and 26% had an NLR value of ≥ 9. In all, 62% presented with gastrointestinal symptoms, and depression was documented in one-third of the subjects at admission. Overall, we recorded a mean weight loss of 0.41 kg (P = 0.038) during hospitalization, with significant weight loss observed among patients hospitalized for 7 days or more (P = 0.009). The bivariate analysis revealed that inflammatory status (P = 0.016) was associated with in-hospital weight loss, while the multivariate analysis determined that the contributing factors were length of stay (P < 0.001) and depression (P = 0.019). CONCLUSIONS We found that inflammatory status of the patient might influence the incidence of weight loss during hospitalization, while depression and length of stay were independent predictors of weight loss during hospitalization.