We propose an efficient method to synthesize large-scale soluble acidified graphitic carbon nitride (g-C3N4). The as-prepared material exhibits the characteristics of a poly-ammonium salt and is soluble in several solvents with good dissolution-recrystallization reversible equilibrium. The pH value- and temperature-dependent solubility of the acidified g-C3N4 facilitates its separation and purification. After dissolution, acidified g-C3N4 forms isolated ultrathin nanosheets, making it an ideal precursor for large quantities of g-C3N4 nanosheets. This study raises the possibility of liquid assembly for g-C3N4 nanosheets based composite materials, expanding the functionalization and application of g-C3N4.