Dialkylated melamine derivatives self-assemble with halogen acids into 2D organic microsheets in organic solvent through counterion bridged multiple hydrogen bonds as well as electrostatic interactions and π–π stacking. Alkyl chains are introduced to suppress the growth in a particular dimension, supplying a general approach for the fabrication of 2D structures. Protonation is demonstrated to be a crucial factor in the formation of 2D assemblies. The assembly and disassembly of microsheets can be reversibly controlled by alternating addition of acid and base. Even the aspect ratio of the rectangular microsheets can be further modulated through the addition of different amounts of acid.