Abstract : Alarmingly, up to 85 % of cancer patients can experience malnutrition during their illness period. Increasing the cancer patients' nutritional knowledge and compliance to the treatment is the ultimate goal for health care providers. Patients with cancer might have no adequate nutrition information. This study was conducted to assess the Jordanian cancer patients' level of nutritional knowledge and determine if their level of information affecting their dietary practices. A cross-section design with structured questionnaire was used. A sample of 140 participants completed the nutrition Knowledge and dietary practices questionnaire. The results showed that majority of the participants had unsatisfactory level of nutrition knowledge (57.5%). The results showed that green leafy vegetables more garlic, carrot, lentil, liquid oil, milk and yoghurt were the most types of food consumed by the participants. The results showed that large percentage of the participants had low Dietary Diversity Scores (DDS) (N= 90, 64.3%), 40 participants had moderate DDS (28.5%), and 10 participants had high DDS (7.2%). The results showed that there was a significant relationship between nutritional knowledge and dietary diversity (r = 0.64. p = (P≤0.05). Furthermore, significant relationship was found between nutritional knowledge and food frequency among the participants in the current study (r = 0.71. p = (P≤0.05). There is a need for structured educational programs to increase the patients' knowledge and modify their dietary practices