Exhaust particulates from diesel engines have become one of the most severe air pollution problems. The filter trap method is used to control diesel exhaust particulates. Hence, we have conducted an evaluation study of filter traps. In order to clarify the trapping performance such as filtration efficiency and pressure drops of the filter, four kinds of cordierite honeycomb type, two kinds of cordierite foam type and a mullite corrugation type filter were tested.For the honeycomb type filters, it is clear that the micro-pore size mainly affects the filtration efficiency and both the micro-pore size and the cell wall thickness mutually affect pressure drop. Furthermore, it was revealed that the pore size affects the filtration efficiency and pressure drop for the foam type filters. The Mullite corrugation type filter showed the highest filtration efficiency.From the experimental results, it was concluded that the mullite corrugation type and the honeycomb type filter of small micro-pore size and thin cell wall thickness are desirable as diesel particulate filters.AS A MEANS FOR the reduction of diesel exhaust particulates, improvement in combustion through engine modification has been studied mainly so far. In the case of more strict requirements such as the 1987 regulation in the United States, it was considered difficult to satisfy the requirements by engine modifications only. At that time studies of reduction processes by the after treatment system began.* Numbers in Parentheses designate References at end of paper.The filter trap method is considered the most promising method for the reduction of exhaust particulates in the exhaust system. This method entails a ceramic filter being set into the exhaust system to temporarily trap exhaust particulates. The trapped particulates are then burnt again when the temperature of the exhaust and the oxygen level reach the point where combustion is possible, after which the particulates are exhausted as gas. The filter remains attached to the engine and is used continuously, repeating the sequence of collection and recombustion of exhaust particulates.The authors are presently carrying out research with the aim of developing a practical filter trap system and method of usage. This report covers the results of examining the collecting ability of three types and seven kinds of filters, as well as a proposal regarding the more efficient filters.