More than fifty experiments were made with model steel frames of two dimensional two story and of three dimensional three story in which girders or a column or both a girder and columns were heated by electric furnaces under a constant heating rate. These experiments made it possible to analyze thermal stress within the steel frame theoretically. Large thermal stress appeared in the frame corresponding to the "binding modulus" of the frame. The structure was more influenced by the thermal expansion generated by the heated girder than by that of the heated column in the elastic region. In some cases the buckling of heated girder or column occurred. And also heated tests of columns in a six story full scale steel frame were made. The local buckling of column occurred from which the whole structure was influenced.