Patient involvement in the management of Diabetes Mellitus is very necessary to achieve treatment goals. Knowing about the disease can encourage patients to become fully involved. Patient knowledge about Diabetes Mellitus and its management is one of important things that family doctor must pay attention to. This study was aimed to describe the level of knowledge of diabetes patients in primary health care. A cross-sectional descriptive study was conducted on diabetes patients in primary health care. We used the purposive sampling method to take the samples. Measuring the level of knowledge used the Diabetes Knowledge Questionnaire (DKQ) which consisted of 24 questions whose validity and reliability had been tested. The sample consisted of 86 diabetes patients, 29.1% were male and 70.9% were female, most of whom were in the productive age group. Almost all respondents (80.1%) had higher education. A moderate level of knowledge was obtained in the majority of patients (65.1%), while some patients (27.9%) had a good level of knowledge. Only a few patients (7%) had poor knowledge. The study could be concluded that knowledge level of diabetes patients in primary health care was at a moderate level. So, continuous and appropriate patient education is necessary to increase patient knowledge.