Nowadays, constructing solid acid catalysts with well-defined structures, environmentally benign, high catalytic activity, easy separation, and high chemical stability is the most important area of industrial and environmental concerns. Over the past few decades, porous conjugated polymers have been employed as stable catalysts support for various organic transformations. Among these materials, graphitic carbon nitride (g-C₃N₄) has been widely studied in the field of photocatalysis and heterogeneous catalysis, due to its high surface area and great physical and chemical stability. Herein, we report the synthesis of sulfonated graphitic carbon nitride (Sg-C₃N₄) as an efficient solid acid catalyst for the preparation of various biologically nitrogen-containing heterocyclic compounds under mild reaction conditions.