Objective: To investigate the association between cysteine level and lumbar spine (LS) bone mineral density (BMD) among children with cerebral palsy, so as to provide a basis for bone health enhancement among children with cerebral palsy. Methods: A total of 149 children aged 10-18 with cerebral palsy who were admitted to the G city Social Welfare Institute (Luogang District) from January 2023 to January 2024. Basic demographic characteristics of children with cerebral palsy were extracted from medical records system. Cysteine levels were measured using the enzyme cycling method. LS BMD of the children was determined by specialized rehabilitation physicians using dual energy X ray absorptiometry, and the corrected BMD Z -scores for LS were calculated. Non restrictive cubic splines and segmented multiple linear regression were employed to analyze the correlation between cysteine levels and age specific height Z -scores (HAZ scores) for LS BMD in children with cerebral palsy. Results: The median cysteine concentration in children with cerebral palsy was 9.13(8.42, 10.30)μmol/L, with significantly higher levels in spastic type children [9.28(8.53，10.49)μmol/L] compared to non spastic types [8.64(7.89，9.66)μmol/L]( Z=-2.46，P <0.05). The median LS BMD HAZ score was -1.07( -2.10 , -0.16), and the detection rate of decreased bone mass was 29.5%. There was an "L" shaped association between serum homocysteine concentration and LS BMD HAZ score in children with cerebral palsy. When serum homocysteine concentration was below 8.7 μmol/L, a significant negative correlation was observed between LS BMD HAZ score and serum homocysteine concentration ( B=-0.32, 95%CI =-1.06 to -0.15, P <0.05). Conclusions The significant negative correlation between cysteine levels and LS BMD in children with cerebral palsy at lower cysteine concentrations, which suggests a potentially higher sensitivity to the influence of homocysteine than healthy children and adolescents, warranting attention even if not reaching the standard of hyperhomocysteinemia.