Background:LMWH as periprocedural anticoagulant during PCI has not been extensively studied yet. The aim of this study is to compare clinical outcomes and complications of enoxaparin, one of LMWHs to those of unfractionated heparin(UH) during elective or primary PCI.Method:Eligible patients(pts) were randomized 1:1 into two treatment arms, either a single IV bolus of enoxaparin(75 IU/kg) or UH(100 IU/kg). Patients who had received any anticoagulants at therapeutic doses when the catheterization was started were excluded in this study. Data on patient characteristics, angiographic complications, laboratory variables and in-hospital and 1-month clinical outcomes were compared between two groups.Result:Of 139pts enrolled in this study, 68 received enoxaparin and 71 did UH. The pts��� demographic and angiographic characteristics(men, weight, creatinine, and target vessel of PCI) were quite similar except for age. Multi-vessel angioplasty was performed in 59(42.8%)pts. At least one stent was implanted in 130(93.5%)pts. Sheath was removed immediately right after PCI except one case and then collagen plug was applied in all cases. There were no siginificant differences of angiographic complications like no reflow, thrombus at the treated lesion site, occlusion of collateral branches, distal embolism, dissection, coronary rupture, or acute closure. Cardiac markers(LMWH group number vs UH group number) including CK(6[8.8%] vs 8[11.3%]), CK-MB(6[8.8%] vs 8[11.3%]), and troponin-I(6[8.8%] vs 10[14.1%]) were slightly increased the day after PCI compared to the last value before the procedure in both groups, but the differences were not statistically significant. 1 patient in enoxaparin arm developed NSTEMI during admission. 4 pts from UH and 3 from enoxaparin had hematoma at the puncture site. No other events were reported at 1-month follow-up call.Conclusion:IV bolus of enoxaparin (75 IU/kg) during PCI appears to be equally effective and safe compared to UH. Considering disadvantages of UH including low bioavailability, unpredictable anticoagulant effect, activation of platelet and the necessity of monitoring aCT or aPTT, enoxaparin could replace UH as a periprocedural anticoagulant in PCI lab.