The　boundary　flux　(J(b))　and　sub　boundary　fouling　rate　index　(alpha)　in　constant　pressure　microfiltration　of　activated　sludge　suspension　from　SBR　were　determined　using　TMP-step　method.　Effects　of　mixed　liquor　suspended　solids　concentration　(MLSS),　stirring　rate　and　the　mean　pore　size　of　the　membrane　on　J(b)　and　alpha　were　also　analyzed　using　the　factorial　experiment　method.　Results　showed　that　the　influence　sequence　of　operating　conditions　on　J(b)　was　as　follows:　mean　pore　size　of　the　membrane　＞　stirring　rate　＞　MLSS　concentration.　Specially,　the　effect　of　shifting　mean　membrane　pore　size　from　0.01　mu　m　to　0.1　mu　m　or　from　0.01　mu　m　to　0.22　mu　m　on　J(b)　was　almost　six　times　or　twice　as　much　as　that　of　increasing　stirring　rate　from　100　rpm　to　300　rpm　in　the　tested　MLSS　concentration　range.　The　fact　that　the　membrane　with　lager　pore　size　was　easy　to　be　internally　fouled　at　the　initial　filtration　period　was　confirmed　by　analyzing　alpha　and　morphologies　of　fouled　membranes.　(C)　2016　Taiwan　Institute　of　Chemical　Engineers.　Published　by　Elsevier　B.V.　All　rights　reserved.