Abstract: The thermal conductivities of carbon fiber/epoxy prepreg, in the directions of perpendicular and parallel to the fiber direction, were determined during its curing process by modulated differential scanning calorimetry (MDSC). During the carbon fiber/epoxy prepreg curing process the binary quadratic function models of thermal conductivity in different directions were set up based on the experimental results, which was used to determine the value of thermal conductivity with the temperature and the cure degree during the curing process. The results show that the thermal conductivity of the T800/epoxy prepreg is 0.85~1.25 W/(m稫) and 1.15~1.40 W/(m稫) in the directions of perpendicular and parallel to the fiber direction. The thermal conductivity of the prepreg decreases with the degree of cure at the same temperature, and increases with increasing temperature in the same degree of cure. The verification results show that the binary quadratic function model of the thermal conductivity will improve the accuracy of the parameters in numerical simulation.