Nuclear decommissioning is the final technical and administrative process in the life cycle of nuclear power operation. Experience over the last decade has demonstrated that in general, the process of decommissioning and its cost evaluation has reached industrial maturity, although specific techniques continue to evolve. Owners and licensees of nuclear power plants are generally responsible for developing cost estimates of decommissioning, and a good understanding of these costs is fundamental for the development of estimates based on realistic decommissioning plans. The use of these techniques in the cost evaluation of the decommissioning of nuclear facilities continues to increase this experience. This research has been carried out keeping in mind to evaluate an economical and feasible cost for the proposed decommissioning plan of CANDU (Canada Deuterium Uranium) reactor. Work is done in the major areas of cost estimations for DECON (immediate dismantling), SAFESTOR (deferred dismantling) and ENTOMB (on site end-state). These alternatives were analysed and SAFSTOR method was recommended for 40+ years old, Canadian designed, first generation CANDU reactor decommissioning. This paper provides a cost estimation for a decommissioning as recommended in the analysis performed. A cost of 200 Million $ is evaluated for SAFSTOR decommissioning alternative of proposed CANDU reactor.