Pharmacy Unit at the hospital has an important role in the prescription review of geriatric outpatient in National Health Insurance (NHI) era. The aim of this study was to analyze the role of pharmacist or a pharmacist's assistant in preventing Drug-Related Problems (DRPs) and the alteration of drugs cost that can be generated through the prescription review of geriatric outpatients under NHI in RSUD Kota Depok. This was an observational, retrospective,  with pre-post study during January to April 2016. The evaluation was carried out on 599 prescription of geriatric outpatient under NIH. In the assessment activities, resulted in cost savings of Rp.1.773.642. The role of pharmacy in conducting drug substitution can save the cost of prescription up to 3,78% of the total cost of a prescription before review. Pharmacist give more recommendations related to drug substitution because of shortages or stocks out and inappropriate prescribing with national formulary and hospital formulary. There was a statistically significant between the prescription cost before and after prescription review by the Wilcoxon test ( p < 0,05 ). To determine the role of the pharmacist in the prevention of DRPs, a discussion group  consists of 4 pharmacists was established. The total cost of a prescription after being given recommendations regarding the DRP through discussion groups is greater than the cost of the previous one. The cost increased to Rp. 97 392. But with this increasement, it can resulted cost avoidance quite significantly by Rp.1.117.843,617.