Objective To assess the clinical equivalence of TQ-Z2301, a biosimilar of adalimumab, to the reference adalimumab in the treatment of Chinese patients with active ankylosing spondylitis. Methods This multicenter, randomized, double-blind, positive-controlled phase III clinical trial was conducted in 19 centers across China. Chinese adults with active ankylosing spondylitis despite being treated with non-steroidal anti-inflammatory drugs for >= 4 weeks were randomized in a 1:1 ratio to subcutaneously receive 40 mg of TQ-Z2301 or adalimumab every other week for 24 weeks. The primary endpoint was the percentage of patients who achieved at least 20% improvement according to the Assessment of Spondyloarthritis International Society criteria (ASAS20) at week 24. The equivalence was established if the 90% CI for RR of ASAS20 between two groups at week 24 fell within (0.80, 1.25). Secondary endpoints included efficacy measures of disease activity, spinal mobility, physical function and quality of life, immunogenicity, and pharmacokinetic parameters. Safety analysis was done for all patients who received at least one study drug. Results A total of 380 patients were enrolled in the study between September 2018 and October 2019, including 188 in the TQ-Z2301 group and 192 in the adalimumab group. In the full analysis population, the ASAS20 response rate at week 24 was 86.70% in the TQ-Z2301 group, and 80.73% in the adalimumab group, the RR of ASAS20 for TQ-Z2301 versus adalimumab was 1.074, 90% CI (0.997, 1.157), fell within the predefined equivalence boundary (0.80, 1.25). Except for the SF-36 at week 12, there was no statistical difference between the two groups for all the secondary endpoints (P>0.05). The incidence of adverse events group was 82.45% in the TQ-Z2301, and 83.85% in the adalimumab group, the safety profile of the two groups was similar. The profiles of immunogenicity and pharmacokinetics were also similar between the two groups. Conclusion TQ-Z2301 is equivalent to adalimumab for the treatment of Chinese patients with active ankylosing spondylitis. The safety, immunogenicity, and pharmacokinetic characteristics of both drugs are similar.