Deep venous thrombosis (DVT) is a major health problem that results in significant morbidity and mortality. Critical care nurses are the key players in the prevention of DVT and its complications. They are in the ideal position to asses' patient risk factors early and ask for DVT prophylaxis. Therefore, the current study was carried out to evaluate the effect of implementing nursing guidelines on the occurrence of DVT in critically ill patients. This study was carried out in four critical care unites in Assuit University Hospitals. The sample of this study consisted of 60patiens divided into two groups G1 (control group) 30 patients and G2 (interventional group) 30 patients. Two tools were used in this study. Tool one "Patient’s assessment for DVT" it consisted of four parts, part I which included the patient’s Profile, Part II that included the risk factors, part III which consisted of special biological factors and therapeutic modalities in the ICU. Part IV that included "Preventive measures check lists for Prevention of DVT" done by the critical care nurses for the control group. Tool two: "DVT evaluation sheet" it consisted of three parts part I "DVT manifestations" and part II "laboratory tests" and part III "Doppler Ultrasound findings" Finding of the current study revealed that low incidence of DVT in the global sample, only two patients experienced DVT in the control group, and none of the interventional group experienced DVT. The preventive measures of DVT done by the critical care nurses for the control group using non pharmacological and mechanical methods were not adequately performed. It was observed that all the studied patients of control group did not were the elastic stocking, while small proportion of this group performed leg exercises, changed their position, did deep breathing, and coughing exercises, and transfer on the chair. It was observed that, most of the studied patients experienced low percent of DVT manifestations with no statistical significant difference between the both groups. The present study reveals also that nearly half of the studied patients were in moderate & high risk grad for DVT in the both groups it was recommended that provide training program to update critical care nurses' knowledge and skills about DVT preventive measures. Repeat this research on a large sample size and in multi centers for generalization.