Background: The proportion of antimicrobial-resistant Enterobacteriales as a causative pathogen of community-acquired acute pyelonephritis (APN) has been increasing. The aim of this study was to quantitatively evaluate the impact of antimicrobial resistance on medical costs and length of hospital stay for the treatment of APN. Materials and Methods: A single-center retrospective cohort study was conducted between January 2018 and December 2019. All hospitalized patients aged ≥19 years who were diagnosed with community-acquired APN were recruited, and those diagnosed with Enterobacteriales as a causative pathogen were included. Log-linear regression analysis was performed to determine the risk factors for medical costs and length of hospital stay. Results: A total of 241 patients participated in this study. Of these, 75 (31.1%) and 87 (36.1%) had extended-spectrum beta-lactamase (ESBL)-producing pathogens and ciprofloxacinresistant pathogens as the causative pathogen, respectively. Based on the log-linear regression model, ESBL-producing Enterobacteriales is a causative pathogen that is, on average, 27.0%, or United States Dollar (USD) 1,211 (P = 0.026) more expensive than non-ESBL-producing Enterobacteriales. A patient who is a year older would incur USD 23 (P = 0.040) more, those having any structural problems in the urinary tract would incur USD 1,231 (P = 0.015) more, and those with a unit increase in the Pitt bacteremia score would incur USD 767 (P <0.001) more, with all other variables constant. Having a case in which ESBL-producing Enterobacteriales is a causative pathogen would explain staying 22.0% longer or 2 more days (P = 0.050) in the hospital than non-ESBL-producing Enterobacteriales. A patient who is 10 years older would, on average, would have to stay for half a day longer (P = 0.045). Any structural problems in the urinary tract explain a longer stay (2.4 days longer; P = 0.032), and moving from 0 to 5 on the Pitt bacteremia score would explain four more days (P = 0.038) in the hospital. Conclusion Patients with community-acquired APN with ESBL-producing Enterobacteriales as the causative pathogen would incur, on average, 27.0% higher medical costs and 22.0% longer hospitalization days than patients detected with non-ESBL-producing pathogens.