Ankylosing spondylitis (AS) is a common inflammatory rheumatic disease that affects the axial skeleton, causes inflammatory lower back pain, and structural and functional disorders, which affect quality of life negatively.The purpose of this study is to investigate the effects of kinesiophobia in AS on pulmonary function tests (PFTs) and functional performance.Thirty-one individuals with AS (n = 19 male, n = 12 female) who were suitable on the basis of the Modified New York (MNY) criteria were included in the study. The participants were given the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Bath Ankylosing Spondylitis Functional Index (BASFI), the Bath Ankylosing Spondylitis Metrology Index (BASMI), in addition to the Tampa Scale for Kinesiophobia (TKS), PFTs, respiratory muscle strength, pain evaluation, and 6-minute walking test (6MWT).The mean values were found as the following: TKS, 41.65 ± 7.59; pain visual analog scale (VAS) score, 6.23 ± 2.86; forced vital capacity (%) (FVC), 75.35% ± 17.92%; forced expiratory volume in first second (%) (FEV1), 73.45% ± 17.20%; FEV1/FVC (%), 75.58% ± 15.99%; peak expiratory flow (%) (PEF), 54,90% ± 20.21%; forced expiratory flow at 25% to 75% (FEF25–75), 77.71% ± 27.05%; maximal inspiratory pressure (MIP), 62.06 ± 31.68; maximal expiratory pressure (MEP), 95.94 ± 36.60; 6MWT, 445.88 ± 99.48. The scores obtained in TKS were found related to the values of FVC (%), FEV1 (%), chest expansion, BASFI, modified Schober test, lumbar lateral flexion, cervical rotation, and total BASMI score (r = −0.43, −0.36, −0.41, 0.42, −0.49, −0.56, −0.52, 0.56, respectively; P < .05).Kinesiophobia is a condition that may arise in individuals with AS, which has negative effects. Physiotherapists have a responsibility to eliminate kinesiophobia beliefs and prefer therapy method in line with this responsibility.