To assess insulation behavior of conventional fireproof materials（such as concrete

gypsum etc.）

or to calculate the temperature response of insulated steel members

thermal conductivity of the materials should be determined.Thermal conductivity of fireproof materials are temperature-dependent

thus applying constant values of thermal conductivity of the materials

which are measured at ambient temperature

to calculate the temperature of insulated steel member in fire condition might yield great errors.But in practice effective constant thermal conductivity i.e.equivalent thermal coductivity of fireproof materials is favorably received.The concept of equivalent thermal conductivity was introduced.This paper also proposes a test method to determine the equivalent thermal conductivity of fireproof materials.Comparison between theoretical and experimental results show that the method is valid and convenient for determining the temperature of insulated steel members in fire.