The discharge and the collection efficiency characteristics of an electrostatic precipitator have been studied under various operating conditions. The specific resistivity of pulverized coal dust was about 1013∼1014[${Omega}{cdot}cm$] and reached the maximum value of 6${ imes}$1013[${Omega}{cdot}cm$] at 150[$^{circ}C$]. Back corona has been occurred as dust contents and gas temperature increase. In the case of back corona occurrence, collection effciency decreased rapidly. This problem has been solved by increasing moisture contents. Experimental results showed that collection efficiency of the full wave voltage was higher than that of the pulse wave voltage. The modification parameter k of the collection efficiency equation was about 0.42.