We aimed to investigate complementary or alternative medicine (CAM) usage and knowledge levels of chemotherapy (CT) receiving cancer patients. Questionnaires about CAM usage and knowledge levels of the patients were completed. A total of 289 patients were included. Median age was 58 (min-max: 21-89) years. Sixty-two of 289 patients (22%) received CAM. Fifty-two patients (18%) thought CAM was beneficial and 237 of them (82%) thought that it was harmful. Sixty-one of them (98%) received CAM orally. Majority of CAMs used were herbal substances. Twenty-eight of the patients (45%) used CAM due to belief of natural products strengthen their body, 16 of them (26%) used CAM due to insistence of their relatives, 8 patients (13%) used CAM with thought of their CT did not benefit and 10 patients (16%) received CAM as a supportive treatment. Thirty-seven patients (60%) received CAM concomitant with CT. Thirty-two patients (52%) did not inform their clinicians while using CAM. Twenty-one (34%) and 45 (73%) of patients had no opinion or knowledge about effects and side effects of CAM they used respectively. Nearly half of the patients did not inform their clinicians about CAM they used. Knowledge level of patients used CAM was poor.