The aim of this work is to compare the efficacy of UFH and LMWH in prophylaxis against postoperative DVT, (i.e. incidence of DVT and PE.) and their SAFETY, (i.e. incidence of postoperative bleeding complications). Also our aim is to assess the accuracy, sensitivity and specificity of Radionuclide Venography (RNV) as an alternative diagnostic tool to Duplex in diagnosis of DVT. This study was carried on 96 patients admitted to the general surgery unit in Kasr Al Aini Hospital – Cairo University, all of them underwent surgical procedures . We detected that the use of LMWH was more effective in reducing the incidence of both DVT and PE rather than UFH and it is safer regarding the incidence of development of post operative wound hematoma or unusual bleeding form the drain sites rather than UFH , i.e. LMWH is more efficient in preventing the development of DVT and PE, and it is more safer than UFH. However, LMWH was found to be much more expensive than UFH .YET UFH remains the time honored cheap standard treatment of DVT. In this study also we tested the efficiency of RNV as an efficient alternative tool to Duplex in diagnoses of DVT, and we found that, the accuracy, sensitivity and specificity are nearly equal in both techniques with superiority of RNV in diagnosing proximal DVT and superiority of duplex regarding distal DVT. RNV was efficient, minimally invasive and safer than contrast venogrphy. Also, RNV was helpful in diagnosing PE in the same setting when Tc 99m –MAA was used as it evaluates the lung perfusion. However RNV is relatively difficult to be applied as a routine examination or to be used as a follow up procedure.