Background and Objectives: Recent study reported transradial approach was feasible for percutaneous revascularization of chronic total occlusion (CTO). Recently introduced 5-French guiding catheter may be limited by less backup support. We investigated the feasibility and safety of 5-French transradial coronary intervention (TRI) of CTO and compared it with 6-French approach. Materials and Methods: One hundred seven patients who underwent TRI for total occlusion (TIMI 0 or 1) for more than 2 months were prospectively included in this study from April 2002 to July 2004. Forty seven patients were included for 5-French group (5F), 60 patients for 6-French group (6F). The clinical, angiographic and procedural characteristics were prospectively evaluated and compared between the two groups. Result: No major difference was noted in clinical characteristics between 2 groups. 5F group was associated with shorter occlusion length (5F: 8.1짹7.8, 6F: 14.7짹12.8, p=0.003) and higher incidence of tapered type of entry morphology (5F: 77%, 6F: 57%, p=0.042). Deep throating technique was more often used in 5F group (5F: 84%, 6F: 53.3%, p=0.001). However, these differences did not affect procedural success rate statistically. There was no significant difference of occlusion duration, lesion calcification, and lesion tortuosity between 2 groups. Procedural success was achieved in 41 lesions (87%) in 5 Fr group and 51 lesions (85%) in 6Fr group (p=0.175). Duration of occlusion, calcification at lesion site, and lesion tortuosity were statistically significant independent predictors for procedural success. Minor hematoma occurred in only 2 case of 5F group. No radial artery occlusion occurred in both group. Conclusion: Five-French TRI may be feasible and safe for the patients with CTO lesions, particularly for those with lesion of low risk for procedural failure.