Abstract: The sequential treatment with alkaline followed by acid was applied to extract insoluble dietary fiber( IDF)from the peel of pitaya and main process conditions were optimized by single- factor experiments combined with response surface methodology. The extraction rate and purity of IDF were investigated with respect to Na OH concentration,alkaline extraction time,alkaline extraction temperature,alkaline extraction liquid- to- material ratio,acid extraction temperature,acid extraction time and acid extraction liquid- to- material ratio. The results showed that the optimal extraction conditions were Na OH concentration of 4.3%( g / g),alkaline extraction temperature46.5 ℃,alkaline extraction time 60 min,alkaline extraction material- to- liquid ratio 15 ∶ 1( m L / g),acid extraction temperature 77.4 ℃,acid extraction time 1.5 h and acid extraction material- to- liquid ratio 15∶1( m L / g).Under the optimal extraction conditions,the yield and purity of IDF were 30.29% and 94.78%,respectively.