Melamine trisulfonic acid (MTSA) as a highly efficient heterogeneous solid acid catalyst catalyzes various organic transformations. The great efforts have been made by many scientists to utilize MTSA as a green catalyst for the preparations of N- and O-containing heterocyclic compounds, for the protections of alcohol, phenols, amines and aldehydes and ketones, for the acetylation of alcohols and phenols and for the N-formylation of amines. The superior advantage of this heterogeneous catalyst is that it can be recovered and reused several times without the loss of their efficiency. In this review, preparation and applications of MTSA in organic synthesis are investigated.