To meet increasing demand for lithium, it is very essential for exploiting the lithium resources dissolved in seawater, groundwater and brine. It’s prospected that extracting lithium from solution with lithium ion-sieve, that is, spinel lithium magnesium oxides. Preparing high effective lithium ion-sieve is the heart of the technology. Magnesium oxide (MnOOH), the precursor (Li1.6Mn1.6O4) and the lithium ion-sieve were prepared successively, and their structure and properties were characterized with AAS, XRD and SEM. The results show that fibrous MnOOH is synthesized via hydrothermal reaction of KMnO4 and ethanol at 120°C for 24 h, and brown Li1.6Mn1.6O4 with little impurity is prepared with the Li/Mn mole ratio 4 after hydrothermal reaction of MnOOH and 4 mol/L LiOH at 120°C for 24 h and roast 4 h at 400°C, then lithium ion-sieve is obtained after washing 24 h with 0.5 mol/L HCl solutions and its adsorption capacity for Li+ reaches 38.26 mg/g, which has considerable potentiality comparing to its theory value. All these suggested that synthesis of single phase Li1.6Mn1.6O4 should be essential for next study on extraction lithium with lithium ion-sieve from seawater, groundwater and brine.