We investigated the up-conversion fluorescence characteristics of the bismuth doped silica fibers with and without Al codopant (BA fiber and BI fiber). Unusual up-conversion fluorescence was discovered in both of these two fibers when excited by pump lasers. After more experiments, it was found that the BI fiber showed more complicated and distinct upconversion spectrum than the BA fiber, but with different and weaker NIR emission as we reported before. And it was implied that the up-conversion fluorescence should be mainly responsible for the Bi2+ ions which was rich in BI fiber. Thus, by properly improve the Al co-doping concentration could alleviate the fluorescence up-conversion thus improve the efficiency of the NIR band fluorescence. Besides, the complicated up-conversion fluorescence bands may helpful to clarify the energy levels of the Bi ions in silica materials.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.