Objective To explore the necessity of inferior vena cava(IVC) filter implantation during catheter directed thrombolysis (CDT) for acute deep vein thrombosis (DVT). Method Ninety-three patients with acute DVT were reviewed from Nov. 2006 to Dec. 2008. There were 35 men and 58 women, age averaging at (60 ±29) year old, treated with CDT followed by percutaneous transluminal angioplasty ( PTA). The course of DVT was from 5 h ～ 15 d (6. 28 ±7.08) d with 80 left lower limbs and 13 right lower limbs involved. Results There were 30 patients with prior IVC filter implanted compared with 63 patients without filters (67. 7% ,63/93). Among the patients without filter, there were 93. 6% (59/63) left lower limbs. DSA was redone after thrombolysis. Seventy-seven iliacfemoral thrombosis was resolved completely and stenosis or occlusion of the iliac vein were found in 90. 9% (70/77) cases. Endovascular treatment was performed in 57 patients. There was no patients suffering from symptomatic pulmonary embolism (PE). PE was found in 3 cases with a filter and 1 case without filter was suspected of PE on pulmonary CTA after treatment. Conclusion It is not necessary to routinely place an IVC filter during CDT for treating DVT on left lower limb when the thrombosis is not involing the IVC.