Background: Older adults experience progressive decline in various organs and changes in pharmacokinetics and pharmacodynamics of the drugs in the body which lead to an increased risk of medication-related problems. Potentially inappropriate medications (PIMs) and medication complexity are key factors contributing to adverse drug events in the emergency department (ED). Objective: To estimate the prevalence and investigate the risk factors of PIMs and medication complexity among older adults admitted to the ED. Methods: A retrospective observational study was conducted among patients aged > 60 years admitted to the ED of Universitas Airlangga Teaching Hospital in January - June 2020. PIMs and medication complexity were measured using the 2019 American Geriatrics Society Beers Criteria® and Medication Regimen Complexity Index (MRCI), respectively. Results: A total of 1005 patients were included and 55.0% (95% confidence interval [CI]: 52 – 58%) of them received at least one PIM. Whereas, the pharmacological therapy prescribed to older adults had a high complexity index (mean MRCI 17.23 + 11.15). Multivariate analysis showed that those with polypharmacy (OR= 6.954; 95% CI: 4.617 – 10.476), diseases of the circulatory system (OR= 2.126; 95% CI: 1.166 – 3.876), endocrine, nutritional, and metabolic diseases (OR= 1.924; 95% CI: 1.087 – 3.405), and diseases of the digestive system (OR= 1.858; 95% CI: 1.214 – 2.842) had an increased risk of receiving PIM prescriptions. Meanwhile, disease of the respiratory system (OR = 7.621; 95% CI: 2.833 – 15.150), endocrine, nutritional and metabolic diseases (OR = 6.601; 95% CI: 2.935 – 14.847), and polypharmacy (OR = 4.373; 95% CI: 3.540 – 5.401) were associated with higher medication complexity. Conclusion: In our study, over one in every two older adults admitted to the ED had PIMs, and a high medication complexity was observed. Endocrine, nutritional and metabolic disease was the leading risk factors for receiving PIMs and high medication complexity.