Recent studies have been directed toward obtaining a better understanding of the application of electrostatic precipitators to collect fly ash particles produced in a coal-fired power plant. Electrical resistivity can be described as the resistance of the collected dust layer to the flow of electrical current and is an important property for the collection efficiency in the electrostatic precipitator. In this paper, fly ash resistivity as a function of temperature up to $450^{circ}C$ has been experimentally investigated using the resistivity meter consisted of the movable electrode, dust cup, and furnace. Resistivity was found to increase with increased temperature up to $200^{circ}C$ due to the reduction of water concentration and then gradually decrease with increased temperature due to the activation of electrons. As the resistivity of fly ash in the flue gas temperature of $150^{circ}C$ was measured >$10^{10}$ ohm cm, the efficiency of fly ash removal in the electrostatic precipitator might be expected to be low due to back-corona phenomenon. Flue gas conditioning in the electrostatic precipitator to reduce the resistivity of fly ash as required.