The purpose of this study is to propose an economical and steady planning model of long-term replacement project on water distribution system to co nsider uncertainty of water demand in future. For economical efficiency as the first objective, the model deals with minimization of expected value of total cost in a planning period. Assuming that uncertainty of future water demand appears as width of estimated cost variation, the second objective is minimization of total cost width. Two LP (Linear Programming) models are defined for the first and the second objectives respectively. Successively, we propose a Fuzzy LP model with two objectives combining each characteristic of the two models. Case study demonstrates that the proposed model has advantage achieving balance of these two objectives well over the two models, and usefulness of the proposed one is confirmed. Furthermore, through comparison of produced plans by the three models, meanings of both economic efficiency and steadiness in the pipeline replacement planning are considered.