BACKGROUND Traditional ankle-foot orthoses (AFOs) are not effective in treating plantar fasciitis, while customized 3-dimensional (3D) printed ankle-foot orthoses are effective in treating many ankle-foot diseases. This study investigated the effects of customized 3D printed AFOs on biomechanics and comfort of the plantar foot in plantar fasciitis. MATERIAL AND METHODS Sixty patients with bilateral plantar fasciitis aged 31-60 years participated in this study. At week 0, patients were randomly assigned into 2 groups: the control group consisting of those wearing separate shoes with prefabricated AFOs; and the experimental group consisting of those wearing a separate shoe and customized 3D-printed AFO. The Footscan® system recorded maximum pressure, maximum strength, and contact area of patients' hallux, toes 2-5, first to fifth metatarsal, midfoot, lateral heel, and midfoot heel at weeks 0 and 8. Patients used visual analogue scale scores at weeks 0 and 8 to assess overall comfort of foot orthosis, to determine the credibility and comfort of both orthopedic insole conditions. RESULTS At week 0, in the experimental group, peak pressure in the hallux and first metatarsal area was significantly higher than the control group (P<0.05), while mid-heel and lateral heel peak pressures were significantly lower than the control group (P<0.05). After 8 weeks, all groups reported more comfort compared with the same group in week 0 (P<0.05). The comfort scores reported by the experimental group were significantly lower than those of the control group (P<0.05). CONCLUSIONS This study supports the efficiency of customized 3D printing AFO for reducing damage associated with plantar lesions and improving comfort in patients with plantar fasciitis compared with prefabricated AFO. Customized AFO is useful in the treatment of plantar fasciitis compared with prefabricated AFOs.