The Affordable Care Act (ACA) expanded Medicaid eligibility to persons with income up to 138% of the federal poverty line. We investigated how Medicaid expansion (ME) impacted the access to cancer-specific surgical care in the US. We used a nationwide population-based database (SEER) to identify patients with the 8 most prevalent cancers between 2007 and 2015. Adjusted difference-in-differences (DiD) and multivariate regression were used for statistical analysis. A total of 1,008,074 patients were included. Patients post-ME were diagnosed at an earlier stage (pre-ME, 27.6%; post-ME, 31.1%; P < 0.001), and lack of insurance coverage decreased from 5.5% to 2.6% (P < 0.001). Lower-SES population had improved access to surgical care (attributable benefit +3.18%; P < 0.001). ME was an independent predictor of access-to-surgery (OR, 1.45; P < 0.001), whereas African-American and Hispanic race were negative predictive factors. After ME, the population without insurance coverage decreased. This was associated with earlier cancer diagnosis and improved access to surgery in patients from economically disadvantaged communities. •The Affordable Care Act extended Medicaid eligibility in the United States.•A higher proportion of cancer patients was diagnosed at an early stage after Medicaid expansion.•Cancer patients living in poor counties had improved access to surgical care.•African American and Hispanic patients still have lower chances to undergo surgical treatment.