Background The excessive use of antimicrobials over the past few decades has led to an ever-increasing spread of microbial resistance, leading to increased cost and time to treat infectious diseases. The aim of this study was to investigate the clinical and economic benefits of an antimicrobial stewardship program on prescribing 5 costly used antimicrobial drugs in a large referral teaching hospital. Methods This study is a quasiexperimental study that focused on the consumption of the 5 costly antimicrobial drugs, including liposomal amphotericin B, caspofungin, colistimethate sodium, linezolid, and voriconazole between preintervention and postintervention plans (2016–2018). If the antimicrobial was not approved by the infectious disease physician, possible alternative medications were used. Indexes, including total consumption rate, per capita consumption, total cost, per capita cost, mortality rate, and length of hospital stay, were measured annually. Results There were 29,268 and 27,704 hospitalized patients that were screened primarily. Among them, 600 patients were eligible for each preintervention and postintervention phases. After the intervention, defined daily dose dropped by 18.23%, 25.51%, 9.56%, and 31.56% for amphotericin B, colistimethate sodium, caspofungin, and voriconazole, respectively. The expenditure of restricted antimicrobials decreased by 34.98% in the postimplementation of antimicrobial stewardship program (P < 0.05). The rates of hospital mortality before (40.3%) and after the intervention (38.6%) were not significantly different (P = 0.285). There is no significant result between the mean ± SD duration of hospital stays before (40.39 ± 33.07 days) and after the intervention (36.17 ± 24.84 days; P = 0.08). Conclusions Our study data suggest that the active contribution of infectious diseases specialist in the antimicrobial stewardship program can significantly reduce the total cost, as well as defined daily dose of high-cost antimicrobial medications along with improving the clinical outcome.