Despite both IRS-1 and IRS-2 are two important adaptor molecules essential for intracellular signaling of insulin and IGF-I, the distinct biological pattern of IRS-2 versus IRS-1 remains as a concernful issue to be clarified. We demonstrated here an important evidence that in 32D myeloid cells expressing the insulin receptor (InR) or selected mutants of the InR, IRS-2, but not IRS-1, is required for promoting the proliferation and inhibiting the granulocytic differentiation, thus restore ERKs phosphorylation and UBF1 stabilization. In addition, unlike IRS-1, IRS-2 can effectively compensate the InR defective signaling and lead to the activation of cell cycle progression and proliferation genes in 32D myeloid cells. These results indicate a predominant role of IRS-2 involved in InR signaling of 32D myeloid cells.