β-PIX, a Rac1/Cdc42-specific guanine nucleotide exchange factor, is known to regulate actin cytoskeleton remodeling during cell migration. Following in utero electroporation of β-PIX-d vectors into neuronal progenitor cells at embryonic day 13.5, analysis at postnatal day 0 revealed the presence of clustered neurons and neurites outside of the marginal zone. This cluster structure was confirmed to be composed predominantly of neurons by the neural marker TuJ1. In vitro, β-PIX-d overexpression promoted neurogenesis and increased Rac1 activity. These findings suggest that β-PIX-d and Rac1 interactions play a critical role in the formation of neocortical clustering and the regulation of neuritogenesis.