1, 4-Dimethyl-3-carbamoylpyridinium chloride (DCP•Cl) has been synthesized as a new fluorogenic reagent for aromatic aldehydes. Aldehydes gave a green fluorescence (λex420-439nm and λem504-519nm) after reaction with DCP•Cl at 37°C for 50min in the presence of alkali and sodium sulfite. The method is simple and sensitive for aromatic aldehydes except for those having hydroxy or dimethylamino group. Aliphatic and arylaliphatic aldehydes and substances other than aldehydes showed no or weak fluorescence. By the proposed method, benzaldehyde, furfural and 4-methoxybenzaldehyde could be determined in the ranges 0.06-3nmol/ml, 0.08- 3nmol/ml and 0.3-6nmol/ml, respectively, with relative standard deviations of 0.5-2.5%.