Although timber is a combustible material, the char layers created on the surface during fires prevent further burning of the inner sections. Taking advantage of this feature, steel-timber composite (a steel plate sandwiched with timber using high strength bolts) section members were developed, expecting steel alone to take the load under fires. In this research, their 45-minute quasi-fire resistive performance was experimentally evaluated applying the standard time-temperature relationships. In the composite sections, the connecting bolts are exposed, which is not influential to the temperature elevation of the steel. The test parameters in the multiple test specimens were the section sizes as well as exposure of the side surface of the steel plates. The maximum steel temperatures in most specimens were below 350 Celsius.