Fundamental turning tests of carbon steels at low cuuting speed are made by using water base cutting fluids in various kinds of tool materials, to investigate the excessive wear phenomenon at the portion near center of tools in machining of holes using water base cutting fluids. From the experiments, the following results are mainly attained: (1) The reasons of tool wear in the low cutting speed will be not attributed to chemical interaction between tool and work due to temperature, but the actions of mechanical attrition. (2) The amount of wear in water base cutting fluids is remarkably different from dry or cutting oils, which is attributed to the differences of falling type of the built-up-edge and type of chip flow. (3) The selections of suitable cutting conditions and tool materials for the work materials are the most significant for using water base cutting fluids at the low cutting speed.