Rapid growth in demand for computational power has led to the creation of large scale data-centers which consume enormous amount of electrical power resulting in high operational cost and emission of carbon dioxide. Virtualization is a promising approach to reduce this power consumption by consolidating multiple virtual servers onto a smaller number of computing resources. But modern Cloud computing environments have to provide high Quality of Service for their customers resulting in the necessity to deal with power-performance trade-off. In this paper an efficient resource management policy for virtualized Cloud data centers is proposed. Power consumption by data-centers can be reduced by leveraging live migration of VMs and switch off idle nodes.