Objective The aim of this study was to evaluate the efficacy and safety of the biosimilar candidate of adalimumab (HS016) compared with adalimumab (Humira) for the treatment of active ankylosing spondylitis. Methods A multicenter, randomized, double-blind, parallel, positive control, phase III clinical trial was conducted at 28 locations in China. Patients with active ankylosing spondylitis were randomized in a 2:1 ratio to subcutaneously receive 40 mg of either HS016 or adalimumab every other week for 24 weeks. The primary endpoint was to achieve at least a 20% improvement (ASAS20) in patients at 24 weeks according to the Assessment of Spondyloarthritis International Society criteria. The secondary endpoint included other efficacy assessment parameters, health evaluations, safety, pharmacokinetic, and immunogenicity parameters. Results Following the random assignment of 648 patients into HS016 (n = 416) and adalimumab (n = 232) groups, no significant difference was found in the ASAS20 response rates at 24 weeks between the HS016 (364/416, 87.5%) and adalimumab (209/232, 90.1%) treatments and the difference between the response rates (- 2.59%; 90% confidence interval [CI] - 6.77 to 1.60) was within the predefined equivalence margin (+/- 15%). There were also no significant differences when the secondary endpoints were compared (all p > 0.05). Similarly, the rates of treatment-emergent adverse events (TEAEs) were not significantly different between the two groups, with most TEAEs being mild to moderate. Only nine severe cases were found, including seven within the HS016 group, three (0.7%) of which were tuberculosis cases. Plasma concentrations of HS016 and adalimumab from weeks 12 to 14 were similar during the steady-state period and steady-state maximal concentration (C-max,C-ss) was equivalent for HS016 (7356.6 ng/mL) and adalimumab (7600.3 ng/mL). The accumulated proportion of patients with positive human anti-human antibodies (HAHAs) at week 24 was 326/412 (79.1%) in the HS016 group and 183/229 (79.9%) in the adalimumab group (p > 0.05), while the accumulated proportion of patients with positive neutralizing antibody (NAb) tests were 72/412 (17.5%) in the HS016 group and 43/229 (18.8%) in the adalimumab group (p > 0.05). Conclusion HS016 resembled adalimumab in efficacy and safety over the 24-week treatment period.