The equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) of five kinds of potato flour were determined by static weighing method at range of 10~35 ℃ and RH 11%~96%, respectively. The suitable isotherm fitting equation were determined with polynomial equation, Modified-Guggenheim- Anderson-deBoer (MGAB), Modified-Halsey (MHAE), and Modified-Oswin (MOE). The maximum allowable moisture content of potato flour during storage was analyzed by polynomial equations, the absolute safe moisture was 10.05% wet basis (w.b.) at 25 ℃ and 60%ERH, and the relative safe moisture was 12.64% at 25 ℃ and 70% ERH. The isosteric heat of sorption of potato flour decreased parabolically and rapidly with the increase of the moisture content to17.5%. Then the isosteric heat decreased slowly with the increase of moisture content. When moisture content was 22%, the isosteric heat of moisture sorption of potato flour was close to that of pure water.