Abstract: Taking furfurly alcohol as objects, the reactions of furfuryl alcohol and formaldehyde in acid and alkali mediums were investigated via using electrospray ionization mass spectrometer (ESI-MS).The results showed that, furfuryl alcohol and formaldehyde was stable under alkaline conditions, it did not produce self condensation structure, and no reaction between furfuryl alcohol and formaldehyde.Under the acidic conditions, No.5 carbon and hydroxymethyl of furfuryl alcohol occurred hydroxylation.At the same time, there were a lot of self condensation polymerization of furfuryl alcohol, which were competitive responses.