Abstract Background Very few studies have investigated the association between providing unpaid caregiving to a spouse and the frailty of caregivers. This study aims to examine the impact of providing spousal care on frailty among the middle aged and older Chinese population. Methods Data were derived from the 2011, 2013, 2015, and 2018 waves of China Health and Retirement Longitudinal Study (CHARLS) including 4,008 participants aged 50 and above. Frailty was assessed using a composite mean score based on 41 indicators according to Rockwood frailty criteria, including self-reported health, medically diagnosed conditions, medical symptoms, functional activities assessment, Activities of Daily Living (ADLs), and Instrumental Activities of Daily Living (IADLs). A growth curve model was employed to investigate the differences in frailty among caregivers and non-caregivers. Results Compared to non-caregivers, spousal caregivers were more likely to have a higher frailty when adjusted for all covariates (Beta=0.010, SE = 0.003, p < 0.001). Furthermore, female caregivers exhibited a higher rate of change of frailty index over time (Beta=0.002, SE = 0.001, p < 0.05) compared to female non-caregivers, while no such effect was found in males. Conclusions The findings of this study reveal that providing unpaid care to a spouse is associated with an increase in the frailty index over time particularly among female caregivers. These insights underline the necessity for Chinese policymakers to develop and implement targeted interventions aimed at reducing burden on spousal caregiving, thereby preventing an increase in frailty among these caregivers. Such measures would also align with the broader objective of promoting healthy ageing. Key messages • Chinese policymakers need to develop and implement targeted interventions to reduce the burden on female spousal caregivers and prevent increased frailty. • Focusing on the frailty of female spousal caregivers is crucial for promoting healthy aging.