Lamellar MgB2 grains were synthesized by Cu-activated sintering at low temperature. We found that the Mg-Cu liquid can provide a constant liquid environment and the formation of lamellar MgB2 grains is attributed to the two-dimensional nucleation and growth mechanism in the liquid-solid interface. According to the analysis on the temperature dependence of resistivity, these lamellar MgB2 grains possess much better grain connectivity than the typical morphology of MgB2 grains synthesized by the traditional solid-state sintering. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.