Background Chronic total occlusion (CTO) intervention is still challenging because of the limited procedural success rate and higher target failure. It is not clear whether different collateral grade will have impact on the angiographic and clinical outcomes of CTO intervention in drug eluting stent (DES) era. Methods A total of 177 patients (pts) underwent CTO intervention were divided into the two groups according to the grade of collateral vessels (collateral grade 2,3 : n=99 pta, Collateral grade 1: n=78 pts). The collateral vessels were graded according to the Rentrop classification. Grade 0 is non filling of collateral channel. Grade 1 is barely detectable filling of collateral channels without opacification of the occluded artery. Grade 2 is partial filling of the CTO artery. Grade 3 is brisk flow that fills the CTO artery completely. In-hospital and 6-month outcomes were compared between the 2 groups. Results The baseline clinical characteristics were similar between the two groups. The overall procedural success rate is similar between the two groups (98% vs 97.9%, p=0.10). Procedural characteristics and procedure related complication were not different between two groups. At 6 months, these two groups had similar clinical outcomes and angiographic outcomes including the rate of binary restenosis, late loss, death, Q-MI, TVR and MACE (Table). Conclusions CTO intervention in the setting of different collateral grade showed similar safety profile, procedural success rate, complication rate and mid-term outcomes, possibly due to high procedural success rate by improved devices, technical development and the DES usage.