Abstract: Preparing manganese-zinc ferrite by hydrothermal method using spent Zn-Mn batteries has been studied to determine the influential factors on preparing process,including hydrothermal pH value,hydrothermal temperature and hydrothermal time,etc.It is shown that pure Mn-Zn ferrite can be obtained at pH value 10,hydrothermal temperature 210 ℃ and hydrothermal time 2～24 h.The crystallization process can be prompted by increasing the reaction time and temperature.It is also found that Fe powder is the suitable material to remove Hg existing in spent Zn-Mn batteries completely.