Objectives: Hospital acquired infection (HAI‘s) contributes to the major burden in the health care system. Most of the nosocomial infections were thought to be transmitted by the hands of the health care worker. The majority of the HAI’s can be prevented by the major precautionary measure that is hand hygiene.. Hand hygiene practices prevents the cross transmission of infections between patients and also it reduces the incidence of health care associated infections.Lack of awareness and knowledge among health care workers regarding the importance, techniques, methods and quality of hand hygiene increases the risk of cross transmission of diseases.Thisstudy is aimed at assessing the knowledge about hand hygiene among nurses in a tertiary care hospital. Materials & Methods: This cross–sectional study was conducted among nurses working at Government Medical College & Hospital, a tertiary care hospital in Chennai. After taking informed consent,50 nurses were selected by random sampling who volunteered to participate in the study were evaluated based on structured questionnaire. The nurses who were not willing to participate in the study were excluded. Knowledge on hand hygiene before and after training was evaluated using WHO hand hygiene questionnaire for health care workers and analyzed using percentages. Results: Before training, a pre test was conducted among the nurses which showed about 50% of knowledge about hand hygiene practices. After training, post test was conducted which showed an increase of 80% knowledge about hand hygiene practices. Conclusion: Knowledge on hand hygiene before training was very poor but it was much better after training session among the nurses.a simple training session can significantly improve the knowledge about hand hygiene among nurses. Hence continual training session has to be conducted among the nurses to reduce the risk of acquiring nosocomial infections.