The orthorhombic Pbn2 1 phase of Li 2 CoSiO 4 has been prepared by solid state reaction of Li 2 CO 3 , CoC 2 O 4 ⋅2H 2 O, and highly dispersed SiO 2 at 900 °C and the subsequent slow cooling in Ar gas stream. The DTA curve shows peaks at around 540 °C indicating a reversible structural phase transition. XRD pattern of the sample quenched from 650 °C can be indexed as a Pmn2 1 phase. However, electron diffraction patterns show complex diffuse scatterings. From the in-situ XRD patterns at high temperature, a reversible second order-type phase transition from Pbn2 1 to Pmn2 1 phase was confirmed and it is interpreted as an order-disorder transition of Co and Li atoms. At high temperature, Pmn2 1 phase transforms to the monoclinic γ-phase with large thermal hysteresis; DTA curve shows peaks at 950°C on heating and at 780°C on cooling.keywords: order-disorder, wurzite-type structure, DTA, high temperature powder XRD, TEM