BACKGROUND: Automated external defibrillators (AEDs) enable laypeople to provide early defi brillations to patients undergoing cardiac arrest, but scant information is available on the general public's ability to use AEDs. This study assessed the ability of laypeople to operate AEDs, the effect of a 15-minute training, and whether skills differed by age. METHODS: From May 1 to December 31, 2018, a prospective simulation study was conducted with 94 laypeople aged 18-65 years (32 aged 18-24 years, 34 aged 25-54 years, and 28 aged 55-65 years) with no prior AED training. The participants' AED skills were assessed individually pretraining, post-training, and at a three-month follow-up using a simulated cardiac arrest scenario. The critical actions and time intervals were evaluated during the AED operating process. RESULTS: Only 14 (14.9%) participants (eight aged 18-24 years, four aged 25-54 years, and two aged 55-65 years) successfully delivered defi brillations before training. AED operation errors were more likely to occur among the participants aged 55-65 years than among other age groups. After training, the proportion of successful defi brillations increased signifi cantly (18-24 years old: 25.0% vs. 71.9%, P<0.01; 25-54 years old: 11.8% vs. 70.6%, P<0.01; 55-65 years old: 7.1% vs. 67.9%, P<0.01). After three months, 26.1% of the participants aged 55-65 years successfully delivered defi brillations, which was signifi cantly lower than that of participants aged 18-24 years (54.8%) and 25-54 years (64.3%) (P=0.02). There were no differences in time measures among three age groups in each test. CONCLUSIONS: The majority of untrained laypeople cannot effectively operate AEDs. More frequent training and refresher courses are crucial to improve AED skills.