Aims: ARHGAP21 is a Rho GTPase-activating protein (RhoGAP) that associateswithmany proteins andmodulates several cellular functions, including actin cytoskeleton rearrangement in different tissues. However, it is unknown whether ARHGAP21 is expressed in pancreatic beta cells and its function in these cells. Herein, we assess the participation of ARHGAP21 in insulin secretion. Main methods: Neonatal mice were treated with anti-sense oligonucleotide against ARHGAP21 (AS) for 2 days, resulting in a reduction of the protein's expression of about 60% in the islets. F-actin depolimerization, insulin secretion,mRNA level of genes involved in insulin secretion, maturation and proliferationwere evaluated in islets from both control and AS-treated mice. Key findings: ARHGAP21 co-localized with actin inMIN6 beta cells and with insulin in neonatal pancreatic islets. F-actinwas reduced in AS-islets, as judged by lower phalloidin intensity. 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