Post-thrombotic syndrome (PTS) occurs in 20-50% of patients with proximal deep vein thrombosis (DVT). In this study, we aimed to identify potential markers of thrombolysis success at the early stage and to clarify the relationship between early thrombolysis success and subsequent PTS development in patients with acute DVT in the iliac vein. Fifty-two consecutive patients with acute iliofemoral DVT who were treated with catheter-directed thrombolysis (CDT) within 21 days of onset were enrolled. An infusion catheter with multiple side holes was placed to cover the thrombosed vessel entirely. Urokinase solution was administered either continuously or with the pulse-spray method at a dose of 480,000-720,000 IU/day over the course of 2-7 days. During CDT, unfractionated heparin (UFH) was infused simultaneously via the access sheath to prevent thrombus formation. Early success was defined as lysis grade ≥ 50% and restoration of forward flow. PTS was diagnosed based on the Villalta scale. Based on the lysis grading method, complete lysis (grade III) was achieved in 8 of 52 (16%) limbs. Lysis grade II (50-99%) was achieved in 35 of 52 (67%) limbs. Lysis grade I (< 50%) was achieved in 9 of 52 (17%) limbs. Therefore, grade II and grade III lytic outcomes (early success) were observed in 43 patients (83%). One-year clinical follow-up was performed for 43 patients (83%). PTS occurred in seven (16%) patients. Early success was more frequently observed in patients without PTS than in those with PTS (92% vs. 43%; P < 0.01). Early success was only significantly associated with PTS in the multivariate analysis. Patients with acute symptomatic iliofemoral DVT who had early success from CDT treatment during the acute phase less frequently progressed to PTS. Patients with early success tended to undergo the pulse-spray method and had a shorter interval from symptom onset to CDT. The use of pulse-spray method and early initiation of CDT since DVT onset were potential markers of thrombolysis success.