Amorphous　solid　dispersion　(ASD)　technology　is　popularly　used　for　enhancing　the　solubility　of　poorly　water-soluble　drugs.　Drug　molecules　in　ASDs　can　be　dispersed　in　the　form　of　either　amorphous　(AASD)　or　molecular　(MASD)　forms.　The　boundary　between　AASDs　and　MASDs　(A-M　boundary)　is　defined　as　the　drug　concentration　at　which　the　existence　of　MASDs　obviously　influences　the　physicochemical　properties　of　ASDs.　In　this　work,　fluorescence　spectroscopy　based　on　the　aggregation-caused　quenching　(ACQ)　phenomenon　was　used　to　determine　the　A-M　boundary　of　curcumin　(CUR)　ASDs　prepared　via　neat　ball　milling.　The　relationship　between　the　fluorescence　intensity　and　the　loading　of　CUR　in　the　sample　is　consistent　with　the　Stern-Volmer　equation.　For　the　CUR　ASDs　with　PVP,　the　samples　with　CUR　loading　below　10%　show　significantly　increased　fluorescence　and　have　a　higher　solubility　(similar　to　178　mu　g.mL(-1)),　suggesting　the　A-M　boundary　is　around　10%.　Similar　A-M　boundaries　around　10%　were　also　observed　for　CUR　ASDs　with　PVPVA,　Soluplus,　HPMC,　and　HPMCAS.　It　is　of　great　significance　to　define　the　A-M　boundary　of　ASDs　for　guiding　pharmaceutical　ASD　formulas　by　balancing　drug　loading,　stability,　and　solubility.