In this paper, the flame-retardant synergistic effect between rare earth oxide and conventional flame retardants (aluminum hydroxide and iron trioxide) has been studied using vertical combustion test. The results show that good flame-retardant synergistic effect exists between them. The composites combining 100 grams of aluminum hydroxide, 40 grams of iron trioxide and 0.8 grams of rare earth oxide can reach FV-0 in vertical combustion test. The thermal stability influence of rare earth oxide to silicone rubber has also been studied by means of thermogravimetric analysis. It has been found that rare earth oxide can function as thermal stabilizer in silicone rubber.