Abstract: The chemical reaction in the process of preparing GdB6 with Gd2O3 and B4C in graphite tube furnace in argon atmosphere was studied. XRD and TG-DTA results showed that the reaction is mainly between the residual impurity C in sample and O2 at the temperature of 367-458°C. In the range from 800°C to 1200°C, there are three reactions in the process, i.e., between Gd2O3 and B4C to produce GdBO3, GdBC and B; among GdBO3 GdBC and B4C to produce GdB4; between Gd2O3 and B4C to produce GdB6. With the rising temperature, the reaction speed of GdB4 increases. The GdB6 is prepared by the reaction of GdB4 with the element B, of which the content of GdB6 is up to 97.8% in 6 h and increases with the prolonged reaction time.