Plate-like ZrB2 grains were synthesized at 1550 degrees C by in situ solid/liquid reaction using Zr and B powders mixed with transition metal (Mo, Nb, Ti, or W) and Si powder. The preferred growth direction of plate grains was along a- or b-axis depending on the initial content of transition metal and silicon in the mixtures. The synthesis mechanism of plate-like grain was possibly related to the catalysis of in situ formed silicides.