The transient hot‐wire method for simultaneously measuring the thermal conductivity and thermal diffusivity of materials has been modified to improve the accuracy of the measurements. In this new experimental method, called the multicurrent method, several constant current values are used for heating the hot wire in order to determine accurately the thermal transport quantities. The details of the multicurrent method are precisely described, and examples of experiments using the method with pure water, electrolytic solution, and ionic conducting glasses are given. It is shown that this method can be used both for liquid and solid materials; a relatively small amount of the specimen material is sufficient for each experiment; the material can be insulating as well as highly ionic‐conductive; the accuracies of the determined thermal conductivity and the thermal diffusivity values are, respectively, around ±1% and ±5%.