Background Emerging evidence suggests that experienced racism might help explain observed ethnic inequalities in early child health and development. There are few studies outside the US context and none that consider mothers' experiences of racism in relation to a range of early childhood health and developmental markers. Methods The authors used cross-sectional data from the UK Millennium Cohort Study on 2136 mothers and their 5-year-old children from ethnic minority groups. Measures of racism tapped two dimensions of mothers' experience: perceived frequency of racist attacks in residential area and interpersonal racism. Markers of child health and development were obesity; socioemotional difficulties; cognitive: verbal, non-verbal and spatial ability test scores. Results There was a suggestion that the mothers' experience of interpersonal racism was associated with an increased risk of obesity ('received insults' OR=-1.47; 'treated unfairly' OR=-1.57; 'disrespectful treatment by shop staff' OR=-1.55), but all CIs crossed 1.0, and size estimates were attenuated on further statistical adjustment. Perception of racism in the residential area was associated with socioemotional difficulties (fully adjusted coefficient=-1.40, SE=-0.47) and spatial abilities (fully adjusted coefficient=-1.99, SE=-0.93) but not with verbal or non-verbal ability scores. Maternal experiences of racist insults were associated with nonverbal ability scores (fully adjusted coefficient=-1.70, SE=-0.88). Conclusion The results suggest that mothers' experienced racism is linked to markers of early child health and development. Interventions that aim to improve early child development and address ethnic health inequalities need to incorporate approaches to tackling racism at all levels of society.