Jianhong, If you did a simple Boost build without restricting the output, then your Boost output directory will have many variants of each library. For example, you will have static and dynamic libraries; libraries with and without debug information, libraries with and without threading. And, for each of the above, you will have a two copies of the library named with and without the Boost version number (e.g., -1_31_1) as a suffix. If you decided what combination of debug/threading/static/version you want, you can delete the others, or at least move them elsewhere. Merrill