Background Trace elements may affect neurodevelopment. There is a lack of data on breast-milk rubidium (Rb) in relation to neurodevelopment in infants. The associations of copper (Cu), zinc (Zn) and strontium (Sr) with neurodevelopment in infants remain uncertain. Objectives We sought to evaluate the associations of breast-milk Rb (primary exposure), Cu, Zn, and Sr with neurodevelopment in infants at age 8 months. Methods The study cohort included 117 breastfed infants. Breast-milk samples were collected at 42 days and 8 months postpartum. Breast-milk Rb, Zn, Cu, and Sr were measured by inductively coupled plasma mass spectrometer. Neurodevelopment was assessed at age 8 months. The primary outcomes were attention and working memory scores, as evaluated by the A-not-B task. Other outcomes included the Mental Development Index (MDI) and Psychomotor Development Index (PDI) as evaluated by the Bayley Scale of Infant Development III. Generalized linear models and restricted cubic spline regression were used to assess the associations between trace elements and neurodevelopment indices. Bonferroni correction was conducted on all data presented. Results A nonlinear association was observed between breast-milk Rb at 42 days and infant's attention at age 8 months (nonlinearity P = 0.037). Positive associations were observed with infant MDI scores and breast-milk Rb at 42 days (beta = 4.46; P = 0.06) and 8 months (beta = 3.79; P = 0.009) postpartum. Breast-milk Zn at 42 days was positively associated with infant's attention (beta = 0.31; P = 0.039). Sr at 42 days was positively correlated with attention (beta = 0.18; P = 0.043) and MDI scores (beta = 2.18; P = 0.015) at 8 months. Inverted U-shape associations were observed for breast-milk Cu at 42 days with infant attention and PDI scores. All associations were not significant after correction for multiple tests. Conclusions Our data suggest that Rb, Zn, Cu, and Sr in breast milk at certain concentrations are associated with neurodevelopment in breastfed infants. Further studies are warranted to validate the findings.