To evaluate the choroidal thickness on acute anterior uveitis in patients with HLA-B27-positive ankylosing spondylitis. In this study, 32 eyes of 16 HLA-B27 positive AS patients with anterior uveitis and age-matched 19 eyes for control group were analyzed between January 2014 and April 2015. Assessment criteria were uveitis activity, visual acuity, flare existence, subfoveal choroidal thickness and central macular thickness measurements. The mean subfoveal choroidal thicknesses in affected eye group (Group 1), unaffected eye group (Group 2) and control group (Group 3) were 348.31±72.7, 301.12±49.2 and 318.0±74.3, respectively, in active periods. (p=0.04 between Group 1 and Group 2, p=0.234 between Group 1 and Group 3) The mean central macular thicknesses of Group 1, Group 2 and Group 3 were 268.50±16.5, 267.31±16.3 and 249.7±30.5, respectively, in active periods. (p=0.84 between Group 1 and Group 2, p=0.029 between Group 1 and Group 3). However, in convalescence period, the mean subfoveal choroidal thicknesses of Group 1, Group 2 and Group 3 were 322.40±48.5, 300.75±47.7 and 318.0±74.3, respectively. (p=0.22 between Group 1 and Group 2, p=0.854 between Group 1 and Group 3) The mean central macular thicknesses of Group 1, Group 2 and Group 3 were 269.75±21.9, 256.62±21.5 and 249.7±30.5, respectively. (p=0.09 between Group 1 and Group 2, p=0.03 between Group 1 and Group 3). In HLA-B27 positive ankylosing spondylitis patients with anterior uveitis, the choroidal thicknesses of the affected eyes were found as thicker than fellow unaffected one or control eyes in active period. The central macular thicknesses are not affected on both active and convalescent period.