Dead-end　microfiltration　experiments　with　the　activated　sludge　suspension　from　submerged　membrane　bioreactors　were　performed　to　determine　the　critical　flux,　which　is　a　very　significant　factor　to　indicate　the　membrane　fouling　in　microfiltration　process.　In　this　study,　the　critical　permeation　fluxes　were　measured　by　successive　variations　of　transmembrane　pressure　(step　by　step　technique)　under　different　operating　conditions　(temperatures,　stirring　rate　and　concentrations　of　the　mixed　liquor　suspended　solid　[MLSS])　using　polyvinylidene　fluoride　membranes　with　a　pore　size　of　0.1　mu　m.　A　study　of　the　impact　of　various　operating　conditions　on　the　fouling　rate　when　the　critical　flux　is　achieved　was　especially　made.　The　experiments　revealed　that:　the　increase　in　stirring　rate　leads　to　a　decrease　in　the　rate　of　fouling;　the　fouling　rate　decreased　with　the　increase　in　temperature　when　it　was　less　than　a　certain　values,　after　that,　it　increased　with　the　continuous　increase　in　temperature,　while　the　variation　of　the　concentration　of　the　MLSS　has　a　negative　influence　on　the　membrane　fouling.　The　results　obtained　from　the　experiments　can　provide　reliable　information　to　the　optimization　of　operating　conditions　to　alleviate　membrane　fouling.