Background: Diabetes is one of the most common chronic and non-communicable metabolic diseases and one of the major public health problems. Lifestyle and diet are remarkable factors in controlling diabetes. Objectives: This study aimed to determine the level of knowledge and stages of nutritional behavior change in diabetic patients. Methods: In this descriptive-analytical study, a simple random sampling method was used to select 330 diabetic patients covered by comprehensive health service centers in Ghayenat city, South Khorasan Province, Iran. The research instrument addressed the participants’ demographic information, knowledge, and stages of nutritional behavior change in diabetic patients. The ordinal logistic regression was used to examine factors affecting behavior change. In this regard, the significance level was set to be P < 0.05. Results: The participants’ mean age was 57.86 ± 11.72 years, and 63.7% of the patients were female. The mean score of knowledge was 15.73 ± 2.61, and 52.8, 16.9, 8.9, 11.3, and 10.1 percent of the participants were in the maintenance, action, preparation, contemplation, and pre-contemplation stages. The ordinal Logistic regression model revealed that the main factors affecting behavior change were knowledge, level of income, and a family member with diabetes (P < 0.05). Conclusions: Given that about two-thirds of diabetic patients take no training course on diabetes, that above forty percent of these individuals have no proper knowledge about the disease, and that half of the patients are in the pre-maintenance stages of behavior change, holding a training course is of paramount importance for patients.