Efficient control of transmission power of secondary users (SUs) in an underlay cognitive radio network (CRN) is needed to limit interference on primary users (PUs). Decision regarding the presence of primary user (PU) helps in controlling transmission power of secondary user (SU). In this paper a scheme on joint power control of SUs is investigated. Power control of SUs to minimize interference on PUs in co-existing network is achieved more efficiently with the improved spectrum sensing decision as obtained through co-operation among a number of cognitive radios (CRs). The maximum allowable transmission powers of secondary users have also been estimated in terms of distance between PU receiver and SUs in a cooperative spectrum sensing framework. © 2012 IEEE.