Coagulation　is　the　best　available　method　for　removing　intracellular　organic　matter　(IOM),　which　is　released　from　algae　cells　and　is　an　important　precursor　to　disinfection　by-products　in　drinking　water　treatment.　To　gain　insight　into　the　best　strategy　to　optimize　IOM　removal,　the　coagulation　performance　of　two　Al　salts,　i.e.,　aluminum　chloride　(AlCl3)　and　polyaluminum　chloride　(PACT,　containing　81.2%　Al-13),　was　investigated　to　illuminate　the　effect　of　Al　species　distribution　on　IOM　removal.　PACT　showed　better　removal　efficiency　than　AlCl3　with　regard　to　the　removal　of　turbidity　and　dissolved　organic　carbon　(Doc),　owing　to　the　higher　charge　neutralization　effect　and　greater　stability　of　pre-formed　Al-13　species.　High　pressure　size　exclusion　chromatography　analysis　indicated　that　the　superiority　of　PACT　in　DOC　removal　could　be　ascribed　to　the　higher　binding　affinity　between　Al-13　polymer　and　the　low　and　medium　molecular　weight　(MW)　fractions　of　IOM.　The　results　of　differential　log-transformed　absorbance　at　254　and　350　nm　indicated　more　significant　formation　of　complexes　between　AlCl3　and　10M,　which　benefits　the　removal　of　tryptophan-like　proteins　thereafter.　Additionally,　PACl　showed　more　significant　superiority　compared　to　AlCl3　in　the　removal　of　＜5　kDa　and　hydrophilic　fractions,　which　are　widely　viewed　as　the　most　difficult　to　remove　by　coagulation.　This　study　provides　insight　into　the　interactions　between　Al　species　and　IOM,　and　advances　the　optimization　of　coagulation　for　the　removal　of　IOM　in　eutrophic　water.　(C)　2018　The　Research　Center　for　Eco-Environmental　Sciences,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.