A carbon nitride heterogeneous catalyst containing rhodium, a method for preparing the catalyst, and a method for preparing acetic acid using the catalyst is disclosed. The heterogeneous catalyst is characterized in that the rhodium metal is contained in carbon nitride which is a support insoluble in a liquid solvent, such as water or alcohol. Thus, the catalyst can easily be separated from a resulting product even by a simple process such as filtration. Accordingly, the carbon nitride heterogeneous catalyst exhibits excellent long-term stability and activity by being capable of overcoming the disadvantages of the method using a conventional homogeneous catalyst and minimizing the phenomenon of rhodium leaching, compared to the results of the conventional homogeneous catalytic reactions. The catalyst can thus be effectively used for the preparation of acetic acid by a carbonylation reaction between methanol and carbon monoxide.