The aim was to determine health literacy and the use of complementary and alternative therapies (CATs) in patients with cancer and to investigate the relationship between CAT usage and health literacy. The study cohort consisted of 250 oncology patients. The Patient Interview Form and the Adult Literacy in Medicine Scale were used for collecting data. The use of at least one CAT was reported by 24% of the patients surveyed. Herbal therapies (32.6%) constituted the most popular method, and the most popular herbal therapy was Nigella sativa (54.6%). A total of 29.8% of the patients using CATs reported using herbal therapies for an enhanced immune system. Illiterate patients and those who live in rural areas/towns displayed low levels of health literacy. Healthcare professionals should investigate patients’ use of complementary and alternative approaches, and health literacy should be improved so that patients can be informed regarding the possible benefits and disadvantages of CATs.