In order to extend a life of ageing ship, it is necessary to make a study on feasibility for extending her planned life. Such feasibility study consists of life assessment with a condition survey/assessment, life prediction technique and availability assessment. Nippon Kaiji Kyokai (NK) has made a basic study for developing life assessment system of ships and offshore structures. The logic of procedures for the life assessment is shown diagrammatically in the paper. On the life assessment, special attention shall be paid to fatigue strength as well as protection of corrosion. In the paper, studies on fatigue strength of hull structures and maintenance procedures for well protection of corrosion are briefly reviewed. A discussion is made on several technical aspects of the assessment of aging ships.