Objective: Exercise is effective in reducing the risk of cancer, and treatment side effects. However, our empirical observations indicate that patients diagnosed with cancer have poor knowledge of exercise in cancer. This study aimed to evaluate cancer patients' knowledge of exercise in cancer.Methods: After a review of the literature, the researchers developed a questionnaire aimed at evaluating knowledge of exercise in cancer. The study included patients with a history of cancer aged >= 18 years. The participants were asked to respond to each item in the electronic survey by selecting "I had no idea", "I have heard of it", or "I know very well".Results: The study included a total of 125 participants with a history of cancer (75 females, 60%; 50 males, 40%), and their mean age was 52.05 +/- 11.50 years. We determined the validity and reliability of the questionnaire before analyzing participants' knowledge of exercise in cancer. Bartlett's test of sphericity and the Kaiser-Meyer-Olkin measure indicated that the data were appropriate for factor analysis (p<0.001). Factor analysis confirmed the structural validity of the questionnaire. Cronbach's alpha was calculated as 0.963, implying reliable internal consistency. Subsequently, we analyzed participants' answers to the questionnaire and observed that the response rate of "I know very well" ranged between 3.2% and 14.4% for different items.Conclusion: We prepared and validated a tool for the measurement of knowledge exercise in cancer. Accordingly, we conclude that cancer patients have inadequate knowledge of exercise in cancer. The developed questionnaire can contribute to assess and improve knowledge of exercise among cancer patients.