Abstract : Malnutrition was a severe and widespread concern among cancer patients. It had a detrimental impact on their prognosis and quality of life. According to studies, 15 percent to 40percent of cancer patients lost weight while undergoing therapy. In individuals with advanced cancer, this number could rise to as high as 85 percent. As a result, early treatment and health education on dietary supplement and behaviors might help patients achieve better outcomes and avoid issues. Of this study were to Assess the Nurses Knowledge toward vitamin d3 and calcium need for patients with Cancer at oncology center in AL-Diwaniyah Governorate. and To Find out the Association Between Certain demographical data and Participation in Training Course with Oncology Nurses' Knowledge. A quasi experimental study design is conducted at Al-Diwaniyah Specialized Oncology Center, from 17th March 2021 to 15th May 2022. For the aim of the study, the researcher created the program and instrument. A non-probability purposive sampling had been consisted of (60) oncologic nurses have been chosen to obtained represent and accurate data. The sample size is (60) nurses, split into two groups, one of which includes of (30) nurses as the study group and the other of which consists of (30) nurses as the control groups. The study groups taking the educational programs that deals with Vitamin D3 and calcium that necessary and recommended for cancer Patients (vit. D3 and ca++) of cancer patients, the control group, on the other hand, has not been subjected to the instructional programs. To obtain data from study participant, the researcher employed the following tool: First part is the socio-demographic variables and second the Nurses knowledge related to The Vitamin D3 and calcium that necessary and recommended for cancer Patients (vit. D3 and ca++). The study instrument's validity was assessed by a group of experts, and its reliability was assessed using the internal consistency approach. To determine the difference between the study the control groups, descriptive analysis and analytical inferential analysis were performed. The study's findings revealed that there is very significant difference in between study group's (pretest and posttests) in terms of (nurse's knowledge of vitamin d3 and calcium of people with cancer), (MEAN ± SD= 2.37±0.451) comparing to the pretest score (MEAN ± SD=1.58±0.402) due to effectiveness of an educational programs. Finally, the study finds that an education program focusing on food for vitamin d3 and calcium of people with cancer has a high chance of success. Training health and medical through continuing nursing and medical education (on job training) of all health care providers including nurses who have a major role in raising the level of patient's awareness about the nutrition and importance of having optimum level of this vitamin D and Ca++, explaining the signs and symptoms of vitamin D and Ca.