Abstract CHAMP1 is a gene associated with intellectual disability, which was originally identified as being involved in the maintenance of kinetochore–microtubule attachment. To explore the neuronal defects caused by CHAMP1 deficiency, we established mice that lack CHAMP1. Mice that are homozygous knockout for CHAMP1 were slightly smaller than wild-type mice and died soon after birth on pure C57BL/6J background. Although gross anatomical defects were not found in CHAMP1−/− mouse brains, mitotic cells were increased in the cerebral cortex. Neuronal differentiation was delayed in CHAMP1−/− neural stem cells in vitro, which was also suggested in vivo by CHAMP1 knockdown. In a behavioural test battery, adult CHAMP1 heterozygous knockout mice showed mild memory defects, altered social interaction, and depression-like behaviours. In transcriptomic analysis, genes related to neurotransmitter transport and neurodevelopmental disorder were downregulated in embryonic CHAMP1−/− brains. These results suggest that CHAMP1 plays a role in neuronal development, and CHAMP1-deficient mice resemble some aspects of individuals with CHAMP1 mutations.