Introduction: The prevalence of diabetes mellitus has risen exponentially over the last three decades, with resultant increase in morbidity and mortality mainly due to its complications. The study aimed to assess the knowledge about the complications of diabetes in diabetic patients. Methods: A cross-sectional observational study was conducted among 100 diabetic patients who attended general health check-up clinic of Tribhuvan University Teaching Hospital. Results: Majority of the female patients (78.8%) had the knowledge of diabetes mellitus. Among them, over half had knowledge that diabetes can cause the problem of cardiovascular, kidney failure and retinopathy .Similarly, four-fifths (80%) of the patients above 40 years of age and majority (92.3%) of the patients with more than 5 years duration of diabetes had knowledge about diabetic complications. Conclusion: Female diabetic patients had slightly more knowledge of complication of diabetes in comparison to their male counterparts. The knowledge of diabetic complication was generally high among the patients above 40 years of age and the patients with more than 5 years duration of diabetes. Even then, sex and age was not associated with the knowledge of the need for annual eye checkup and specific diabetic complications such as, kidney and cardiovascular problem, hypoglycemia, neuropathy, foot problem, retinopathy, diabetic ketoacidosis and stroke. However, duration of patient’s diabetics was associated with their knowledge regarding cardiovascular problem, eye check-up annual and retinopathy but was not associated with kidney problem, hypoglycemia, neuropathy, foot problem, diabetic ketoacidosis and stroke. In order to make patient along with their family knowledgeable about the diabetes and its complications, there is need to incorporate diabetes counseling and education activities in General Health Check Up Clinic.