Multispectral　bioluminescence　tomography　(BLT)　attracts　increasing　more　attention　in　the　area　of　small　animal　studies　because　multispectral　data　acquisition　could　help　in　the　3D　location　of　bioluminescent　sources.　Generally,　BLT　problem　is　ill-posed　and　a　priori　information　is　indispensable　to　reconstruction　bioluminescent　source　uniquely　and　quantitatively.　In　this　paper,　we　propose　a　spectrally　solved　bioluminescence　tomography　algorithm　with　an　optimal　permissible　source　region　strategy.　Being　the　most　different　from　earlier　studies,　an　optimal　permissible　source　region　strategy　which　is　automatically　selected　without　human　intervention　is　developed　to　reduce　the　ill-posedness　of　BLT　and　therefore　improves　the　reconstruction　quality.　Furthermore,　both　numerical　stability　and　computational　efficiency　benefit　from　the　strategy.　In　the　numerical　experiments,　a　heterogeneous　phantom　is　used　to　evaluate　the　proposed　algorithm　and　the　synthetic　data　is　produced　by　Monte　Carlo　method　for　avoiding　the　inverse　crime.　The　results　demonstrate　the　feasibility　and　potential　of　our　methodology　for　reconstructing　the　distribution　of　bioluminescent　sources.　(C)　2008　Optical　Society　of　America