The factors associated with sustained virologic response (SVR) in chronic hepatitis C (CH-C) genotype 1 patients treated with simeprevir (SMV), pegylated interferon (Peg-IFN) plus ribavirin (RBV) triple therapy have not been fully investigated. Two hundred and twenty-nine treatment-naïve CH-C patients treated with SMV triple therapy were enrolled in this study. The overall SVR rate was 87% in per-protocol analysis. In multivariate analysis, the interleukin (IL) 28B genotype (rs8099917, TT vs. non-TT, odds ratio [OR]: 0.044, P = 0.001) and RBV dose (< 10/10–12/ ≥ 12 mg/kg/day, OR: 4.513, P = 0.041) were significant factors associated with SVR. In patients with the IL28B non-TT genotype, RBV dose affected SVR dose-dependently in stratified analysis of RBV dose (P = 0.015); it was 44% (8/18) for patients administered <10 mg/kg/day of RBV, 78% (14/18) for those administered 10–12 mg/kg/day of RBV, and 100% (3/3) for those administered ≥12 mg/kg/day of RBV, whereas in patients with the IL28B TT genotype, a significant correlation between SVR and RBV dose was not observed (P = 0.229). Regarding RBV dose reduction of less than 10 mg/kg/day, the inosine triphosphate pyrophosphatase (ITPA) genotype (rs1127354, CC vs. non-CC, OR: 0.239, P = 0.003) and age (by 1 y.o., OR: 1.084, P = 0.002) were significant independent factors. RBV dosage affected SVR dose-dependently in patients with the IL28B non-TT genotype treated with SMV triple therapy. Special attention to anemia progression and RBV dosage should be paid to aged patients with the ITPA CC genotype.