The GTPase-activating protein (GAP) specific to the small GTPase Arf6, ACAP3, is known to regulate morphogenesis of neurons in vitro. However, physiological significance of ACAP3 in the brain development in vivo remains unclear. Here, we show that ACAP3 is involved in neuronal migration in the developing cerebral cortex of mice. Knockdown of ACAP3 in the developing cortical neurons of mice in utero significantly abrogated neuronal migration in the cortical layer, which was restored by ectopic expression of wild type of ACAP3, but not by its GAP-inactive mutant. Furthermore, morphological changes of neurons during migration in the cortical layer were impeded in ACAP3-knocked-down cortical neurons. These results provide evidence that ACAP3 plays a crucial role in migration of cortical neurons by regulating their morphological change during development of cerebral cortex. (C) 2017 Elsevier Inc. All rights reserved.