The objectives of this study were to evaluate the reliability of Bath ankylosing spondylitis functional index (BASFI) and Bath ankylosing spondylitis disease activity index (BASDAI) in Chinese ankylosing spondylitis (AS) and undifferentiated spondyloarthropathy (USpA) patients. 664 AS patients by the revised New York criteria for AS and 252 USpA patients by the European Spondyloarthropathy Study Group criteria were enrolled. BASDAI and BASFI questionnaires were translated into Chinese. Participants were required to fill in BASFI and BASDAI questionnaires again after 24 h. Moreover, BASDAI and BASFI were compared in AS patients receiving Enbrel or infliximab before and after treatment. For AS group, BASDAI ICC: 0.9502 (95% CI: 0.9330-0.9502, α=0.9702), BASFI ICC: 0.9587 (95% CI: 0.9521-0.9645, α=0.9789). For USpA group, BASDAI ICC: 0.9530 (95% CI: 0.9402-0.9632, α=0.9760), BASFI ICC: 0.9900 (95% CI: 0.9871-0.9922, α=0.9950). In the AS group, disease duration, occipital wall distance, modified Schober test, chest expansion, ESR, and CRP showed significant correlation with BASDAI and BASFI (all P<0.01). In the USpA group, onset age, ESR, and CRP were significantly correlated with BASDAI (all P<0.05), while modified Schober test, ESR, and CRP were significantly associated with BASFI (all P<0.05). The change in BASDAI and BASFI via Enbrel or infliximab treatment showed a significant positive correlation (P<0.01). The two instruments have good reliability and reference value regarding the evaluation of patient's condition and anti-TNF-α treatment response.