Predictors of neoatherosclerosis in patients who received primary percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) remain unclear. The aim of this study is to investigate the frequency and risk factors of neoatherosclerosis 1-year after the onset of ACS. This study investigated 83 patients who underwent PCI for ACS followed by 1-year follow-up optical coherence tomography. The patients were categorized into the neoatherosclerosis (n = 11) and non-neoatherosclerosis groups (n = 72). Baseline characteristics, PCI procedures, medical therapies, and blood tests at 1-year, including detailed lipid profiles, were compared between the two groups. Diabetes mellitus was more prominent in the neoatherosclerosis than in the non-neoatherosclerosis group (45% vs. 17 %, respectively, p = 0.03). Total cholesterol (171 ± 37 mg/dL vs. 145 ± 25 mg/dL, respectively, p < 0.01), non-high-density lipoprotein cholesterol (HDL-C) (124 ± 36 mg/dL vs. 94 ± 24 mg/dL, respectively, p < 0.01), low-density lipoprotein cholesterol (94 ± 36 mg/dL vs. 72 ± 19 mg/dL, respectively, p < 0.01), and lipoprotein (a) (Lp[a]) (70 [19-112] mg/dL vs. 10 [3-25] mg/dL, respectively, p = 0.03) at follow-up were significantly higher in the neoatherosclerosis group. Multivariate analysis revealed that neoatherosclerosis was associated with high serum non-HDL-C (odds ratio [OR]: 1.075; 95 % confidence interval [CI]: 1.011-1.144; p < 0.01) and high serum Lp(a) levels (>30 mg/dL) (OR: 11.0; 95 % CI: 1.492-81.02; p = 0.02). Poorly controlled non-HDL-C and Lp(a) would be risk factors of neoatherosclerosis in patients 1-year after ACS.