Novel　1-1.5　mu　m　BiOCl0.5Br0.5　composite　microspheres　were　prepared　by　coprecipitation　method,　then　calcined　at　different　temperatures.　The　BiOCl0.5Br0.5　samples　before　and　after　calcination　were　characterized　by　powder　x-ray　diffraction,　thermogravimetric　analysis,　N-2-physical　adsorption,　scanning　electron　microscopy,　Fourier　transformed　infrared　spectroscopy,　and　UV-Vis　diffuse　reflectance　spectroscopy.　The　photocatalytic　activity　of　the　samples　was　evaluated　by　photocatalytic　degradation　of　Rhodamine　B　under　visible　light　irradiation.　The　results　showed　that　the　thermostability　of　BiOCl0.5Br0.5　composite　microspheres　is　lower　than　BiOCl　and　higher　than　BiOBr.　Heat　treatment　at　low　500　degrees　C　could　obviously　improve　the　crystallinity　of　BiOCl0.5Br0.5　microspheres,　resulting　in　a　significant　increase　in　activity.　BiOCl0.5Br0.5　microspheres　calcined　at　450　degrees　C　displayed　the　highest　activity　and　stability.　At　elevated　temperature　calcination　(600-800　degrees　C),　phase　transition　occurred　over　BiOCl0.5Br0.5.　Br　element　was　gradually　lost　and　new　phase　of　Bi24O31Br10　appeared.　High　temperature　calcination　did　not　change　the　morphology　of　BiOCl0.5Br0.5,　but　the　surface　area　and　surface　OH　groups　decreased,　which　resulted　in　a　large　decrease　in　activity.