Background: Patients with diabetes mellitus (DM) type 2 in the world reach 90% of all patients with diabetes. That was caused of poor diet. Healthy diet is the key therapy of DM type 2 and is affected by diet and patient compliance which is influenced by family support and levels of knowledge. Objective: To determine the knowledge of family diet on patient with DM in Puskesmas Kasihan I Bantul working area. Methods: The study design was descriptive analytic with cross sectional method and univariate analysis. The population was 276 people and the sample was 45 people. The sampling technique used cluster sampling used a questionnaire made by researchers and have tested the validity used pearson product moment on 48 people with r tables 0.368 and reliability test used KR 20 with the result of 0,812.The study was conducted in Puskesmas Kasihan I Bantul working area Results: The majority of family knowledge was in low category. Family knowledge based on age in enough category at 36-60 years. Family knowledge based gender was in low category in woman. Family knowledge based on education level was in enough category at SMA. Family knowledge based on employment status was in low category for respondents who does not ocapation. Family knowledge based on the information exposure was in enough and low category for respondents who have never got information. Conclusion: The level of respondent kwonledge in Puskesmas Kasihan I Bantul working area was in low category. Suggestion: Puskesmas can provide information more detail for families about diet of patients, especially on provide the amount of the patients’ diet.