To determine associations between physical activity (PA), sedentary behavior (SB) and oxidative stress in colorectal cancer patients, ColoCare Study participants in Germany wore an accelerometer 6- and/or 12-months post-surgery. Spearman partial correlations were used to assess associations between PA and urinary concentrations of oxidized guanine, a validated marker of oxidative stress. There were no significant associations between PA or SB and oxidized guanine in n=76 measurements (ng/mgcreatinine; r=0.03, p=0.76 for PA, r=-0.05, p=0.69 for SB). Novelty: Objectively-measured physical activity was not associated with a marker of oxidative stress in colorectal cancer patients.