A new methodology is being introduced to address the life-cycle cost (LCC) of base-isolated large liquefied natural gas (LNG) tanks. The relationship between LCC and seismic fortification intensity was established to evaluate how much earthquake force being isolated can minimize LCC. Each composition of LCC was analyzed including the initial cost, the isolators' cost, and the excepted damage cost. The isolators' cost consists of the cost of laminated lead rubber bearings (LLRB) and supplemental dampers. The cost of LLRB was proposed proportional to its volume and the proposed cost of supplemental dampers was not only related to its maximum displacement but also to its tonnage. The concept of seismic intensity was being used to estimate the expected damage cost, greatly simplifying the calculation. Moreover, a tank in a LNG receiving terminal in China was employed as an example, the LCC of which was assessed in isolated and nonisolated situation, respectively. The results showed that the proposed method was efficient and the expected damage cost was enormously reduced because of the application of isolation, which leaded to the reduction of the LCC of the tank.