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　(~178　μg·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.　©　2025　by　the　authors.