As a prelude to scaled-up deployment of electric vehicles, this paper examines the economic feasibility of replacing the current fleet of fossil fuel taxis in Seoul with electric vehicle (EV) taxis by phasing the former out based on their opertional lifetime. In the cost-benefit analysis for such a transition, costs of purchasing vehicles and constructing and maintaining charging infrastructure are estimated based on the market prices and characteristics of taxi transport in Seoul. On the benefit side, the avoided environmental costs due to reduced air pollutants and greenhouse gas emissions are calculated. The transport planning model, especially traffic assignment, is incorporated in the calculation process for a better estimation of the avoided costs through more accurate link flows and speeds on the road network. Savings from the fuel switch to electricity from liquefied petroleum gas for taxis are also estimated. The resultant benefit-cost ratio signifies economic viability of the deployment of EV taxis. The results of the study are encouraging and could be a good piece of rationale to push forward with electric vehicles. That will be even more so if decreasing battery costs and shortening charging time come into play.