Background <p>Temperature extremes are established triggers of cardiovascular events in the general population, while cancer patients face elevated atrial fibrillation (AF) risk due to disease- and treatment-related factors. However, whether cancer confers additional vulnerability to temperature-related AF events remains unclear. This study aimed to examine the association between extreme temperatures and AF hospitalizations in cancer patients compared with non-cancer controls.</p> Methods <p>Data were derived from the real-world study of the Chinese AF registry (2014–2023), comprising 1,665,014 AF hospitalizations. This study is an exploratory, cancer-focused secondary analysis of the RWS-CAF registry. Overall associations between ambient temperature and AF hospitalization in the full registry have been reported separately. We used a time-stratified case-crossover design with distributed lag nonlinear models to assess temperature-AF associations. Cancer patients (<i>n</i> = 243482) were compared with demographically matched non-cancer controls, and unmatched analyses were performed in the full cohort. Subgroup analyses examined effect modification by age, sex, and geographic region.</p> Results <p>Extreme cold (1st percentile, − 5.6&#xa0;°C) was associated with higher AF hospitalization risk in cancer patients (RR 1.80, 95% CI 1.60–2.03) compared with matched non-cancer controls (RR 1.27, 95% CI 1.21–1.34; <i>P</i>_{<i>interaction</i>} &lt; 0.001). The nonoptimal temperature-attributable fraction was also higher in the cancer group (19.7%) than in matched non-cancer patients (10.2%), with cold exposure accounting for the majority of the burden. Among cancer patients, the cold-related RR was higher in males (1.86, 1.62–2.15) than in females (1.37, 1.26–1.50; <i>P</i>_{<i>interaction</i>} &lt; 0.001), and the cold-related RR was higher in northern than in southern China (<i>P</i>_{<i>interaction</i>} = 0.002). Lag-specific analyses suggested earlier onset and more persistent cold-related risk elevation in the cancer group.</p> Conclusions <p>Patients with cancer appeared more vulnerable to cold-related AF hospitalization than those without cancer, with stronger associations observed in men and in northern regions. These findings support the possibility that cancer modifies the temperature–AF relationship and warrant confirmation in studies with prespecified analyses and more detailed oncologic characterization.</p> Graphical Abstract <p></p>