Nogo-A, a member of the reticulon family, is one of the most important myelin-associated inhibitors for axonal growth, regeneration, and plasticity in the central nervous system. RhoA has been targeted pharmacologically to promote neurite outgrowth and functional recovery in the brain and spinal cord. However, the underlying mechanism of the inhibition of neurite outgrowth by Nogo-A has not yet been fully defined. Protein kinase B (PKB, also known as Akt) is a protein serine/threonine kinase that plays a key role in intracellular signaling and cellular homeostasis. This study reports the role of PKB signaling on Nogo-A-treated PC12 neuronal cells. An inhibitory fragment of Nogo-A (Nogo-66) activated RhoA and reduced the phosphorylation of PKB at Ser473 in a time-dependent manner. In contrast, pretreatment with Y27632, a specific inhibitor of Rho-A, resulted in an increase of the phosphorylation of PKB. Nogo-66 also inhibited the neurite outgrowth of PC12 cells, whereas pretreatment with LY294002, a specific inhibitor of PKB, ameliorated the neurite outgrowth. These data suggest that PKB is involved in the inhibition of neurite outgrowth by Nogo-A in PC12 cells.