This study aimed to investigate the association between age and the risk of 30-day unplanned readmission among adult patients with acute myocardial infarction (AMI) undergoing percutaneous coronary intervention (PCI).This retrospective analysis included patients from the Nationwide Readmissions Database with AMI who underwent PCI during 2013-2014. We used multivariable logistic regression model to calculate adjusted odds ratios (AORs) for risk of readmission. To examine potential non-linear association, we performed logistic regression with restricted cubic splines (RCS).Of the 492550 patients with AMI aged above 18 years undergoing PCI during the index hospitalisation, 48630 (9.87%) were readmitted within 30 days. Although the crude readmission rate of younger patients (aged 18-54 years) was the lowest (7.27%), younger patients had higher risk of readmission compared with patients aged 55-64 years for all-causes (AOR 1.06 (1.01 to 1.11), p=0.0129) and specific causes, such as AMI and chest pain (both cardiac and non-specific) after adjusted for covariates. Patients aged 65-74 years were at lower risk of all-cause readmission. Older patients (age 75 years) had higher risk of readmission for heart failure (AOR 1.50 (1.29 to 1.74)) and infection (AOR 1.44 (1.16 to 1.79)), but lower risk for chest pain. RCS analyses showed a U-shaped relationship between age and readmission risk.Our results suggest higher risk of readmission in younger patients for all-cause unplanned readmission after adjusted for covariates. The trends of readmission risk along with age were different for specific causes. Age-targeted initiatives are warranted to reduce preventable readmissions in patients with AMI undergoing PCI.