Poly (tetrafluoroethylene) (PTFE)/Salt alginate (SA) flat membranes were prepared from a mixture of PTFE concentrated dispersion and Sodium alginate (NaAlg) aqueous solution. The chemical constitutions of the PTFE/SA membranes before and after sintering were investigated with FTIR. Meanwhile, TGA and contact angle to water were utilized to analyze the thermal stability and hydrophobic property. Moreover, effects of sintering conditions on the properties and morphologies of the membranes were also investigated. Results showed that SA was decomposed in the sintering process, and the membranes maintained excellent thermal stability and strong hydrophobicity. In addition, it was beneficial for the membranes to obtain high air flux by short sintering time and the membranes had different surface morphologies by different cooling rates.