Phosphoinositide signaling is implicated in many important cellular events including peptide hormone induced-signal transduction, actin polymerization and cell migration. Several studies proposed that INPP4B (Inositol Polyphosphate Phosphatase 4B) which converts PtdIns(3,4)P2 to PtdIns(3)P is a tumor suppressor. However, some recent studies have suggested the oncogenic role of INPP4B. For such reasons, INPP4B is emerging as an important and dynamic player in cancer. Here, we investigated the function of INPP4B and how Akt activity is controlled by INPP4B. We observed how INPP4B affects cell physiology including cell migration through the regulation of phosphoinositide. The biochemical method to detect oxidized cysteines showed that H2O2 induces the oxidation of INPP4B in a concentration-dependent manner and serine mutation of catalytic cysteine of INPP4B (Cys842 into Ser842) blocks INPP4B oxidation. To investigate the relationship between INPP4B oxidation by H2O2 and conversion of phosphoinositides, we monitored the dynamic change of the level of PtdIns(3,4)P2, a main substrate of INPP4B by intracellular H2O2. The level of PtdIns(3,4)P2 is increased in the plasma membrane under PDGF stimulation. Intriguingly, inducible expression of INPP4B decreased Akt(Ser473) phosphorylation specifically under oxidative stress. Using fluorescence imaging, we investigated whether PtdIns(3,4)P2-dependent recruitment of Lpd (Lamellipodin) can contribute to actin polymerization. We found that PtdIns(3,4)P2 is associated with Lpd at the leading edge of lamellipodium. Furthermore, inducible expression of INPP4B decreased the amount of Lpd and the intensity of branched actin networks. To analyze the cell migratory behavior, we conducted wound healing assay. Inhibition of oxidized INPP4B elicited the reduction of wound closure. Taken together, we propose that INPP4B tumor suppressor is inactivated by H2O2 and selectively acts as a regulator for Akt (Ser473) activation through conversion of phosphoinositides. Furthermore we suggest that oxidation of INPP4B tumor suppressor is implicated in actin polymerization and cell migration by controlling PtdIns(3,4)P2 levels.