The　extraction　methods　of　six　different　extracellular　polymeric　substances　(EPS)　were　studied　on　activated　sludge　sampled　from　an　aeration　tank.　Results　showed　that　the　thermal-alkaline　method　gave　the　highest　extraction　values　(64.95　mg·g-1),　followed　by　sodium　hydroxide,　a　cation　exchange　resin,　and　the　thermal　method,　while　ultrasonication　and　the　sulfuric　acid　method　resulted　in　relatively　low　extraction　values　(below　10　mg·g-1).　In　addition,　the　extracted　EPS　contained　more　carbohydrates　than　proteins.　To　optimize　the　extraction　conditions　of　the　thermal-alkaline　method,　the　effect　of　pH,　water　bath　temperature,　and　water　bath　time　on　the　extraction　were　investigated　through　an　orthogonal　experiment.　The　optimum　conditions　were　determined,　as　follows:　pH　of　13,　water　bath　temperature　of　80℃,　and　water　bath　time　of　10　min.　The　highest　extraction　values　in　terms　of　proteins　(29.55　mg·g-1)　and　carbohydrates　(33.37　mg·g-1)　were　achieved　under　the　optimum　conditions.　©　2016,　Science　Press.　All　right　reserved.