Background Post- embolization syndrome is a common complication after transarterial chemoembolization (TACE) for hepatocellular carcinoma (HCC). N-acetylcysteine (NAC) is known to ameliorate liver damage from several causes. Aim To determine the efficacy of intravenous NAC in the prevention of post-embolization syndrome in HCC patients following TACE. Methods In this study, patients with HCC admitted for TACE were prospectively enrolled. All patients were randomized stratified by Child A or B to receive NAC or placebo. The NAC group received intravenous NAC 24 h prior to TACE (150 mg/kg/h for 1 h followed by 12.5 mg/kg/h for 4 h, then continuous infusion 6.25 mg/h for 48 h after the procedure). The placebo group received an infusion of 5% glucose solution until 48 h after procedure. The post- embolization syndrome was defined as: T = 38.5 c and serum ALT > 3 times of pretreatment value. Results In total, 111 HCC patients were enrolled; 57 were randomly assigned to NAC group and 54 to placebo group. The incidence of post-embolization syndrome was lower in NAC group (24.6%) compared to placebo group (48.2%); P = 0.01. On multivariate analysis, receiving IV NAC (P = 0.03) and HCC diameter (P < 0.01) were associated with developing post-embolization syndrome. Post-TACE liver decompensation was documented in 26/111 (23.4%) patients. There was no difference in the incidence of post-TACE liver decompensation between NAC and placebo group. Conclusions In this study, intravenous NAC administration reduces the incidence of post-embolization syndrome after TACE in patients with HCC. However, it does not prevent post-TACE liver decompensation.