Abstract: p27^kip1 is a versatile cyclin-dependent kinase inhibitor, which blocks the G₁/S conversion and negatively regulates cell cycle by inhibiting CDK activity. p27^kip1 gene has been shown to play dual roles to both promote and inhibit oncogenesis. This double-sided nature of p27^kip1 is also reflected in its subcellular localization, which is regulated by phosphorylation at multiple sites. Such knowledge might be of prognostic value and offer novel therapeutic windows. This paper summarizes the role of p27^kip1 subcelluar localization in tumor researches, the effect of phosphorylation on p27kip1 subcelluar localization and the value of p27^kip1 in tumor therapies and prognosis.