As an important trace element in human bone, zinc (Zn) has a great influence on bone metabolism. The aim of this work was to prepare a Zn-containing material that can release Zn ions. For this purpose, submicrometer willemite phase zinc silicate (Zn2SiO4, ZS) with poor crystallinity was synthesized at 110°C via the microwave-assisted hydrothermal (MH) method. Under the MH condition, the growth of ZS was consistent with “multi-core growth” mechanism. Moreover, the influences of the reaction temperature and the reactant concentration on the final products were investigated in detail. The inductively coupled plasma atomic emission spectroscopy (ICP) data indicated that the poor crystallinity ZS could successfully release Zn for at least 28 d as soaking in the simulated body fluid (SBF). Without the replenishment of SBF, ~333 μM Zn was released from ZS synthesized at 110°C (ZS-110). If SBF was periodically replenished once a day, more Zn was released from ZS-110, and the parascholzite phase calcium zinc phosphate hydrate (CaZn2(PO4)2·2H2O) formed during the soaking process of ZS-110. Under the concentration of 6.25 mg/mL, the extract of ZS-110 was proved to be nontoxic by assessing with mouse osteoblast cells (MC3T3). Therefore, the poor crystallinity ZS has potential to be incorporated into the orthopedic reconstructive materials as a source of Zn ions, which can improve the bioactivity of the materials.