Background: Chest drain is a tube inserted through the chest wall between the ribs and into the pleural cavity to allow drainage of air, blood, and fluid or pus out of the chest. Aim: The study aimed to evaluate nurses' performance regarding new guidelines of a chest drain. Design: A descriptive exploratory research design was utilized in this study. Sample: Two samples were taken. First sample Includes group (A) of 56 patients with a chest drain, and group (B) included all available nurses working in cardiothoracic and chest ICUs (35) nurses . Setting: the study was conducted at cardiothoracic and chest ICUs in Mansoura University Hospital, which includes 45 beds. Data Collection: 1) Patient assessment questionnaire composed of three parts, this tool filled by the researcher from patient files and from inspecting the patients. 2) Nurses' self-administered questionnaire composed of two parts. 3)Nurses' practice observational checklist composed of two parts. Results: 94.3% of studied nurses got unsatisfactory level of knowledge, 71.4% of the studied nurses got satisfactory level of practice regarding new guidelines of a chest drain in ICU. The main results: There was a strong positive statistically correlation between nurses' total level of practice and their total level of knowledge. Conclusion: Less than third of the studied nurses got satisfactory level of knowledge regarding new guidelines of chest drain in ICU. On the other hand, more than two thirds of the studied nurses got satisfactory level of practice regarding new guidelines of chest drain in ICU. Recommendations: Increase the number of nurses staff because nurses shortage affect patient outcomes and Encourage nurses to attend online courses and workshops regularly about new guidelines of chest drain, Also developing booklet by simple language about new guidelines of chest drain for nurses who provide care for patients with a chest drain .