OBJECTIVES: Nosocomial infection can occur more frequently in patients on admission to the hospital. Patients must result in a longer treatment stays, and increase costs from the use of antibiotics to treat patients. The purpose of this study was aimed to calculate the value of antibiotics used to treat patients with nosocomial infections in inpatient department at Nakhon Pathom hospital. METHODS: The data collection of antibiotic use's expenditure for nosocromail infection treatment at in-patient department was performed between 1 January 2010 to 30 June 2010. The source of information came from Infectious Control division of the hospital. All information were recorded further source such as in-patient data-based was used if the information of former source was incompleted. RESULTS: The analysis showed that patients with nosocomial infection is 314 patients (141 male,173 female). The most age of infection is between 71-80 years (31.53%). Building that has the most infected frequency is female medicine building (infected 35 patients (11.15%)).The most common pathogen is Acinetobacter baumannii-MDR (25.34%) while the most origin of infection is lower respiratory tract (62.80%). Duration of admission in hospital until the occur of nosocomial infection is during the first 10 days (32.80%).The value of all antibiotics used to treat patients is 12,354,176.50 bath and the cost of each month as shown in Figure 1. Sulbactam and Cefoperazone (Sulperazon®) is the most highest cost, our data is similar trend from previous study in other setting. Figure 1 Cost of antibiotics used in each month (data for 6 months). CONCLUSIONS: From the information obtained from this study will make the hospital concern about strategies to prevent nosocomial infection to reduce the loss of various and enhance the quality of life for patients.