The p34(SEI-1) oncoprotein is involved in a transcriptional regulation, cell cycle regulation, apoptosis, development and many other important cellular functions. Our present study suggests that p34(SEI-1) can promote metastasis by enhancing migration and invasion of cancer cells. Consistently, p34(SEI-1) expression was found to be increased as the tumor invasiveness progressed in human breast tissues. p34(SEI-1) may promote cancer metastasis by activating the PI3K/AKT signaling pathway. In this process, p34(SEI-1) activates two different serine/threonine kinases, AKT or ILK, depending on the expression status of HER2/neu oncogene. In HER2/neu suppressed cancer cells, p34(SEI-1) promoted metastasis mainly by activating AKT via phosphorylation of the 473 serine residue. In HER2/neu expressing cancer cells, p34(SEI-1) overexpression downregulates HER2/neu expression, leading to the activation of another crucial serine/threonine kinase ILK due to phosphorylation of the 178 threonine residue instead of AKT. These results suggest that p34(SEI-1) affects cancer metastasis by regulating two different signaling pathways depending on the HER2/neu expression level, in which AKT and ILK modulation can be stimulated by p34(SEI-1) overexpression.