Mixing　oppositely　charged　polyelectrolytes　and　multivalent　counterion　solutions　at　low　concentrations　leads　to　the　formation　of　colloidal　ionically　crosslinked　polyelectrolyte　particles.　Due　to　the　rapid　reaction　kinetics,　the　complexation　processes　and　the　final　product　could　vary　significantly　when　changing　the　mixing　efficiency,　which　was　often　overlooked　in　previous　studies.　To　investigate　the　effect　of　mixing　on　the　polyelectrolyte-based　colloid　formation,　we　use　chitosan/tripolyphosphate　mixtures　as　a　model　system　and　compare　the　particle　formation　under　flash　nano-complexation　(FNC,　representing　rapid　and　efficient　mixing)　and　conventional　dropwise　mixing.　It　turns　out　that　the　non-uniform　mixing　and　rapid　complex　formation　during　conventional　mixing　lead　to　particle　formation　at　a　low　tripolyphosphate　:　chitosan　ratio,　which　could　be　avoided　by　FNC.　When　mixing　using　FNC,　the　particle　formation　started　at　a　critical　tripolyphosphate　:　glucosamine　ratio,　below　which　only　soluble　complexes　exist,　and　such　a　critical　ratio　is　independent　of　the　chitosan　molecular　weight　and　charge　density.　Homogeneous　mixing　also　leads　to　the　formation　of　a　large　amount　of　small　primary　particles　without　further　aggregation　due　to　the　rapid　consumption　of　free　crosslinking　counterions.　Such　a　strong　dependency　of　ionically　crosslinked　polyelectrolyte　colloid　formation　on　the　mixing　efficiency　was　also　demonstrated　using　other　polyelectrolytes　and　counterions.　Thus,　the　mixing　efficiency　could　have　a　significant　impact　on　the　interpretation　of　the　complexation　process　and　the　mechanisms　and　should　be　carefully　discussed　when　studying　ionically　crosslinked　polyelectrolyte　colloids.