Background: TB is one of the major causes of morbidity and mortality in the Horn of Africa with Ethiopia carrying a heavy burden. Malnutrition is a critical yet underestimated factor in susceptibility to infection. Infection saps the individual of energy, which reduces productivity at the community level and perpetuates an alarming spiral of infection, disease and poverty. Hence, it is essential to address the nutritional requirements of TB patients. Lack of knowledge about nutritional care and support as well as dietary practice among patients and health care providers aggravated the situation and most patients also reported loss of appetite during their illness. Objective: To assess the knowledge of TB patients and determinants on recommended nutritional care, support and dietary practice during treatment in Addis Ababa, 2017. Method: An institution based cross sectional study was conducted with the total sample size was 525. The study conducted on randomly selected 3 sub-cities and 12 health centers with high TB patient flow. Data were collected using pretested structured questioner. The data was entered and analyzed by SPSS version 21. Bivariate and multivariate logistic regression analyses were done to identify factors that associate with dependent variables. Result: From all TB patient respondents 69.9% had poor knowledge on recommended nutritional care and support which significantly associated with their age (AOR=0.183 95% C.I 0.058,0.580)(p value 0.004)and DDS (AOR=0.027 95% C.I 1.151,9,902)(p value 0.027) and from all participants 71.8% have poor dietary practice which significantly associated with sex (AOR=2.091 95% C.I 1.140,3.836)(p value 0.017) and dietary counseling (AOR=0.055 95% C.0.023,0.135)(p value 0.001). Conclusion: Knowledge on recommended nutritional care and support for TB patients and dietary practice is poor, regular nutritional assessment and dietary counseling of all TB patients should be the part of routine care for TB patients.