摘要Background Under-five mortality(U5M)is a critical public health challenge in low-and lower-middle-income countries(LLMICs),where over 90％of global deaths occur.Despite progress,the changing contributions of risk factors to U5M in LLMICs remain unexplored.Methods We analysed Demographic and Health Survey(DHS)data from 24 LLMICs across two periods:1997-2005 and 2016-2022.We included 139,890 live births in 1997-2005 and 319,034 in 2016-2022.A mixed-effects robust Poisson regres-sion model with a log link function was employed to identify risk factors of U5M in each period.Population-attributable fractions(PAFs)were calculated and compared to investigate changes in the contributions of risk factors over time.Results U5M attributable to never having been breastfed increased by 15.5 percentage points(95％CI 8.6,22.9),early maternal age at birth(＜20 years)by 5.4 percentage points(95％CI 3.1,5.7),and plural births by 1.2 percentage points(95％CI 0.4,1.8).U5M reductions attributable to maternal secondary education were increased by 5.5 percentage points(95％CI 0.4,11.0)and tertiary education increased by 2.6 percentage points(95％CI 1.6,4.2).However,U5M reductions associated with 1-3 antenatal care(ANC)visits decreased by 7.2 percentage points(95％CI 2.4,11.7).Conclusions The main contributors of U5M in LLMICs were never breastfeeding,short birth intervals(＜33 months),ANC uptake,higher maternal education(secondary and tertiary),advanced maternal age at birth(≥35 years),early maternal age at birth(＜20 years),very small infants at birth,male sex,plurality,and single motherhood.The contributions of risk factors to U5M have changed over time.Interventions need to prioritise promoting breastfeeding,enhancing maternal education and increasing ANC uptake,and addressing other significant contributors to U5M.