Attitudes towards cancer may affect the cancer prevention behaviors of cancer patients’ relatives and their participation in cancer screening. Knowing the factors affecting attitudes will shed light on the education programs to be planned to encourage individuals to gain a positive attitude towards cancer and positive health behaviors in cancer prevention. Determining the behaviors towards cancer prevention and cancer screening, identifying reasons that prevent participation in cancer screening, determining the factors associated with the attitudes of cancer patients’ relatives towards cancer, determining the factors affecting their attitudes towards cancer of cancer patients’ relatives, can increase the awareness of healthcare professionals and patient relatives on the subject. The aim of the present study was to determine cancer prevention and early diagnosis behavior and the factors affecting the attitudes of towards cancer of cancer patient relatives. The descriptive and analytical study was completed with 321 relatives of cancer patients. The data were collected by the face-to-face interview method. The interview was conducted in a quiet place, alone with the participant, using a clear and simple language, allowing people to speak freely, and avoiding criticism and evaluation. About half of the participants smoked (49.5%), many did not do regular physical activity (67.3%) or protect themselves from the sun (77.3%), and only 10.9% had regular screening tests. The reasons for not having a screening test were ignorance, disregard, lack of complaints, and fear. Acording to binary logistic regression analysis, the determinants included factors of negative attitudes toward cancer with the age of the patient (Exp(β): 1.024), low education level (Exp(β): 2.572), being the child (Exp(β): 8.484) or sibling (Exp(β): 8.801) of the patient, not being protected from the sun (Exp(β): 2.063), and not doing physical activity (Exp(β): 1.744). Even for those having positive health behaviors, such as not smoking (Exp(β): 2.008) and using sun protection (Exp(β): 2.280), the attitudes towards cancer were negative for the Impossible to Recover sub-dimension. Cancer prevention behaviors and regular participation in cancer screening of cancer patients’ relatives were very low. It was determined that low education level, increasing age of the patient, and the degree of relation to the patient negatively affected attitudes towards cancer, and that there was a need for education. We believe that the results of the present study will contribute to evidence-based practice for cancer prevention and early diagnosis.