Ethnopharmacological　relevance:　The　herbal　decoction　is　a　complex　dispersion　system　containing　solutes,　colloid,　aggregates,　emulsions　and　precipitates.　In　which　phase　bioactive　phytochemicals　are　dispersed　determines　their　delivery,　action　and　metabolism.　This　study　took　ephedrine,　a　well-studied　and　widely　used　phytochemical,　as　an　example　to　elucidate　its　exact　distribution　in　the　phases　of　Ma-Xing-Shi-Gan-Tang　decoction　(MXSGT),　which　is　an　Ephedra　sinica　Stapf.　containing　traditional　Chinese　medicinal　formula,　and　the　biological　meaning　of　this　distribution　correspondingly.　It　may　provide　an　important　update　to　the　safety　and　efficacy　assessment　of　the　herbal　decoction　and　its　active　phytochemicals.　Materials　and　methods:　In　this　study,　the　decoction　was　fractionated　with　size-exclusion　chromatography　coupled　with　multi-angle　laser　light　scattering　detector.　The　morphology　of　fractionated　nanoparticles　was　observed　with　AFM　and　SEM.　The　bioactivities　of　the　decoction,　the　ephedrine　alkaloids　loaded　NPs　(prepared　by　chromatography　isolation)　and　the　synthetic　ephedrine　were　assessed　by　cell　proliferation　tests　using　five　cell　lines,　namely　Caco-2,　L-02,　Hep-G2,　NR-8383,　and　Hela-229.　Results:　Nanoparticles　with　radii　of　gyration　ranged　from　50　to　150　nm　were　isolated,　in　spherical　shape.　Further　analysis　of　nanoparticles　on　the　subsequent　reversed　phase　chromatography　revealed　that　the　majority　of　ephedrine　(99.7%)　and　pseudoephedrine　(95.5%)　were　associated　with　these　nanoparticles,　rather　than　dispersed　freely　in　the　real　solution.　The　addition　of　both　the　herbal　decoction　and　the　separated　ephedrine-loaded　nanoparticles　reserved　higher　cell　viability/proliferation　than　that　of　the　sole　synthetic　ephedrine　among　the　Caco-2,　L-02,　Hep-G2,　and　NR-8383　cells.　In　contrast,　the　nanoparticles　reduced　the　proliferating　power　of　ephedrine　on　Hela-229　cells.　In　general,　the　ephedrine-loaded　NPs　conducted　the　intermediate　influences　on　the　cell　viability,　in　either　way.　Conclusions:　The　colloidal　nanoparticles　were　separated　from　the　decoction.　The　association　of　ephedrine　alkaloids　with　nanoparticles　was　demonstrated　and　may　have　changed　the　bioactivity　of　the　alkaloids.　The　naturally　occurred　colloidal　nanoparticles　may　play　an　important　role　in　the　pharmacological　properties　of　both　the　decoction　and　its　active　phytochemicals,　therefore　warrant　further　studies.　(c)　2013　Elsevier　Ireland　Ltd.　All　rights　reserved.