Objective To investigate the roles of Pipeline embolization device ( PED) in combination with coils in the treatment of large and giant unruptured internal carotid artery aneurysms. Methods From January 2014 to December 2016,51 patients with large (diameter 10-25 mm) and giant (diameter >25 mm) internal carotid artery aneurysms treated at the Department of Neurosurgery,Xuanwu Hospital,Capital Medical University were analyzed retrospectively. Among them,35 were females and 16 were males, the average age was 53 ±13 years (range 15-71). They were divided into a PED group (n=31) and a PED combined with coil group (n=20) according to whether using coils for packing aneurysm cavity or not. The treatment of two groups of patients and ≥6 months of imaging follow-up effect were analyzed. The embolic rate was evaluated by Raymond grade. Results Thirty-one patients with 32 aneurysms ( mean diameter 15 ± 3 mm) in the PED group were treated with 33 PEDs,including 15 with cavernous sinus aneurysm and 17 with supraclinoid aneurysm;20 patients with 21 aneurysms ( mean diameter 17 ± 4 mm) were treated with 22 PEDs in the PED combined with coil group,including 10 cavernous sinus aneurysms and 11 supraclinoid carotid aneurysms. Six months after procedure,imaging follow-up revealed that the incidence of residual aneurysm ( Raymond grade Ⅱ-Ⅲ) in the PED group was significantly higher that that in the PED combined with coil group (9. 7% [n =3] and 0％,respectively). The incidence of thrombosis in PED combined with coil group was significantly higher than that in the PED group,there was significant difference between two groups (P<0. 05). Conclusions When using PED to treat large and giant internal carotid artery aneurysms,packing aneurysm cavity in combination with coils can reduce the incidence of residual aneurysm,but it may have a higher risk of thrombotic events. A prospective randomized controlled trial of large samples is still needed to prove it.