Filamin (FLN) regulates many cell functions through its scaffolding activity cross-linking cytoskeleton and integrins. FLN was shown to inhibit integrin activity, but the exact mechanism remains unclear. Here, we report on the regulation of platelet integrin αIIbβ3 signaling by the FLNa subtype. Three FLNa deletion mutants were overexpressed in the erythro-megakaryocytic leukemic cell line HEL: Del1 which lacks the N-terminal CH1-CH2 domains mediating the FLNa-actin interaction; Del2 lacking the immunoglobulin-like (Ig) repeat 21 which mediates the FLNa-β3 interaction; and Del3 lacking the C-terminal Ig repeat 24, responsible for FLNa dimerization and interaction with the small Rho GTPase involved in actin cytoskeleton reorganisation. Fibrinogen binding to HEL cells in suspension and talin-β3 interaction in cells adherent to immobilized fibrinogen were assessed using the PKC agonist (phorbol 12-myristate 13-acetate) also to activate αIIbβ3. Our results show that FLNa-actin and FLNa-β3 interactions negatively regulate αIIbβ3 activation. Moreover FLNa-actin interaction represses Rac activation, contributing to the negative regulation of αIIbβ3 activation. In contrast, the FLNa dimerization domain which maintains Rho inactive, was found to negatively regulate αIIbβ3 outside-in signaling. We conclude that FLNa negatively controls αIIbβ3 activation by regulating actin polymerization and restraining activation of Rac, as well as outside-in signaling by repressing Rho.