Cilostazol, a phosphodiesterase III inhibitor, is known to have anti-proliferative activity. We investigated the effects of cilostazol 200 mg, in addition to aspirin 100 mg and clopidogrel 75 mg, on carotid intima-media thickness (IMT) progression during a 2-year follow-up period in patients with acute coronary syndrome (ACS) requiring stent implantation. Patients with ACS (n = 130) were randomly assigned to the cilostazol group (n = 64) or the control group (n = 66). Longitudinal images of left and right carotid IMT were measured at baseline, at 6, 12, and 24 months using a 10-MHz linear vascular probe. The primary endpoint was to compare the changes in maximum carotid IMT at 2 years. Other parameters such as inflammatory markers [interleukin (IL)-6, tumor necrosis factor (TNF)-α, C-reactive protein (CRP), and adiponectin] and bleeding risk were also compared. The carotid IMT showed no significant progression from baseline in the cilostazol group compared to significant progression in the control group at 12 months (0.78 ± 0.38 and 0.85 ± 0.41 mm, p = 0.034, respectively) and 24 months (0.82 ± 0.41 and 0.96 ± 0.39 mm, p = 0.022, respectively). Major bleeding (p = 1.00), minor bleeding (p = 0.68), and total bleeding rates (p = 0.74) were similar between the two groups during the 2-year follow-up. Decreases from baseline in IL-6 (-2.79 ± 2.83 and -2.14 ± 3.36 pg/ml, p = 0.010, respectively) and TNF-α (-2.81 ± 1.97 and -2.21 ± 2.68 pg/ml, p = 0.029, respectively) were significantly greater in the cilostazol group than the control group during the follow-up. Cilostazol treatment, with greater anti-inflammatory effect, inhibited the progression of carotid IMT without increasing the risk of bleeding in patients with ACS during the 2-year follow-up.