To provide a simple method for producing protocatechualdehyde in high yield by which the stirring properties during a reaction are improved without using toxic chlorine gas.

This method for producing the protocatechualdehyde represented by formula (2) is carried out as follows. Piperonal represented by formula (1) is reacted with phosphorus pentachloride in the presence of oxygen in an organic solvent. Water is then added to the resultant reaction liquid and further reacted.