Background: Axial spondyloarthritis (ax-SpA) increases the risk of osteoporosis and vertebral fractures (VFs). Although bone mineral density (BMD) is used to diagnose osteoporosis, it has some limitations in patients with ax-SpA. Trabecular bone score (TBS), a new tool that indirectly assesses bone microarchitecture, can be used to assess fracture risk; however, few studies have been conducted to investigate TBS in ax-SpA patients.Objectives: To compare TBS between ax-SpA patients and 1:1 sex- and age-matched healthy controls and determine factors associated with low TBS in ax-SpA patients. Methods: A cross-sectional study was conducted in two tertiary-care hospitals. A total of 137 ax-SpA patients and controls were enrolled. Demographics, disease characteristics, and osteoporosis-related factors were recorded. TBS and BMD at the lumbar spine and hip were measured by dual X-ray absorptiometry (DXA). Low TBS define as a TBS value <1.230. Vertebral fractures were evaluated by densitometric vertebral fracture assessment. Factors associated with low TBS were examined by logistic regression.Results: Most ax-SpA patients were male (75.9%) and tested positive for HLA-B27 (88.3%). The mean (SD) age was 42.8 (12.0) years. The mean (SD) of TBS in the ax-SpA patients was lower than those in the controls [1.402 (0.107) vs 1.440 (0.086), respectively; p=0.002]. The mean (SD) of lumbar BMD in the ax-SpA patients was higher than those in controls [1.186 (0.212) vs 1.087 (0.124), p<0.001], whereas the mean (SD) of femoral neck BMD in the ax-SpA group was lower than that in the controls [0.867 (0.136) vs 0.904 (0.155), p=0.038]. High disease severity as indicated by sacroiliac joint fusion and a high ASDAS score were associated with low TBS with the odds ratios (95% confidence interval) of 11.8 (1.2-115.4) and 5.2 (1.6-16.9), respectively. Conclusion: Ax-SpA patients had a higher prevalence of low TBS than controls. Sacroiliac joint fusion and a high ASDAS score were associated with low TBS.