Objective : We evaluate the effect of the copolymer-coated coils on immediate occlusion of the aneurysm, preventing rupture, and decreasing compaction or re-growth. Methods : Thirty-five aneurysms treated between September 2003 and December 2004 using Matrix detachable coil were reviewed. Study population consisted of 12 men and 23 women ranging in age from 34 to 75 years[mean, 55.1 years]. Twenty-two aneurysms were ruptured and 23 aneurysms were located in the anterior circulation. Follow-up angiography was obtained in 16 patients after 6 months from the procedure. Results : Initial complete occlusion was achieved in 17 aneurysms[48.6%], and the others remained as a residual neck in 8 aneurysms[22.8%] and residual sac in 10 aneurysms[28.6%]. Among these incompletely occluded aneurysms, 7 aneurysms were performed follow-up angiography. And 6 of them converted into complete occlusion. In the other hands, among 17 aneurysms achieved complete occlusion initially, 9 aneurysms were performed follow-up angiography. Recurrence due to coil compaction occurred in one aneurysm and the others maintained complete occlusion. There was one mortality case due to thromboembolic complication. Conclusion : In spite of difficulty in achieving complete occlusion with Matrix coil system, there is no rupture or re-rupture during follow-up period. Follow-up angiography shows many conversions of residual sac into complete occlusion. Embolization using Matrix coil system is safe and effective, but the effects of PGLA copolymer need further investigation.