Objective: To explore the possible factors influencing lumbar spinal bone mineral contents and bone mineral densities in Chinese adolescents with early ankylosing spondylitis(AS). Methods: Thirty-one male Chinese adolescent outpatients with early AS were included and compared with 31 age-matched male controls. Age (year), height (cm), total body weight (kg) together with body mass index (BMI, kg/m2 ) of all subjects and disease duration (month), BASMI,BASFI, BASDAI, SASSS as well as ESR (mm/h) of AS patients were obtained. Lumbar2-4 bone mineral content (L2-4BMC, g) and lumbar2-4 areal bone mineral density (L2-4 BMD, g/cm2 ) were evaluated using dual-energy X-ray absorptiometry (DEXA) with Lunar DPX-IQ device and lumbar2-4 volumetric bone mineral apparent density (L2-4 BMAD, g/cm3 )was subsequently calculated. Correlation and multiple regression analyses were performed. Results: Compared with 31 agematched male controls, AS patients had significantly lower L2-4 BMD [ (0. 984 ± 0.142) g/cm2 vs ( 1.055 ± 0. 137) g/cm2,P = 0.049 ] and L2- 4 BMAD [ (0. 1527 ± 0. 0173) g/cm3 vs (0. 1630 ± 0. 0195) g/cm3, P = 0. 032 ]. In AS patients,multiple regression analysis identified that only the factor of height was significantly correlated with L2- 4 BMC ( R = 0. 673,P = 0.000) and the factor of weight had predominant influences on L2-4 BMD ( R = 0. 620, P = 0. 000) as well as L2-4BMAD (R=0.510, P = 0.003). Conclusion: The young patients with early AS had marked reduction in lumbar spine bone mineral densities, which indicated an important primary event leading to osteoporosis. Positive effects of height and weight on lumbar spine bone mass and densities could expectantly make favorable contributions to early prevention of AS associated bone loss and subsequent osteoporosis.