Background <p>Lung cancer is one of the most frequently diagnosed cancers, and the leading cause of cancer deaths worldwide. Surgical resection is the primary curative treatment. The World Health Organization (WHO) recommends that all adults, including cancer survivors, should engage in at least 150 to 300&#xa0;min of moderate-intensity aerobic physical activity per week. Positive associations have been found between self-reported physical activity and health-related quality of life (HRQoL) after lung cancer surgery. However, there is a lack of studies concerning objectively measured physical activity levels, and longer follow-ups are also missing. This study investigated the relationship between objectively measured physical activity levels and HRQoL in patients 3 and 12 months after lung cancer surgery.</p> Methods <p>Utilizing a cross-sectional design, patients were followed up 3 (<i>n</i> = 83) and 12 (<i>n</i> = 57) months after lung cancer surgery. HRQoL was assessed with the cancer-specific questionnaire EORTC QLQ-C30 and the lung-cancer-specific module LC13. Physical activity was measured with a tri-axial accelerometer (ActiGraph GT3X+).</p> Results <p>At 3 months after surgery, 51% (<i>n</i> = 42) of the patients reached the level of physical activity recommended by the WHO; the corresponding result at 12 months was 42% (<i>n</i> = 24). Patients who reached the recommended level of physical activity reported a better HRQoL, with better global health status and physical function as well as lower symptoms of fatigue, at both 3 and 12 months postoperatively.</p> Conclusions <p>Physical activity was positively associated with HRQoL. Encouraging and supporting patients to engage in regular physical activity could contribute to better HRQoL after lung cancer surgery.</p> Trial registration <p>The trial was registered at ClinicalTrials.gov (NCT01961700), registration date 20,131,009.</p>