PURPOSE: To readily and industrially purify pyrroloquinolinequinone (PQQ) useful as a medicine, etc., in a large amount by treating a culture fluid of a microorganism capable of producing the PQQ with a hydrophilic polyvinyl based anion exchange resin, etc.

CONSTITUTION: A strain of Pseudomonas P2-3, etc., is cultivated in a culture medium containing methanol, etc., at about 30°C for about 6 days to provide a culture fluid containing produced PQQ. The resultant culture fluid is then passed through a column of a hydrophilic polyvinyl based resin substituted by diethylaminoethyl (DEAE) groups to adsorb the PQQ on the resin. The adsorbed PQQ is subsequently eluted with a salt solution in ≤0.5 M concentration, such as NaCl, to afford an eluate, which is then passed through a column of a nonpolar highly porous polymer based resin to adsorb the nonpolar highly porous polymer based resin to adsorb the PQQ on the resin. The adsorbed PQQ is subsequently washed with an aqueous solution of HCl, etc., at about pH2 to remove impurities. The resin is then eluted with water or a water-soluble organic solvent containing ≤50wt.% methanol and purified to recover the aimed pyrroloquinolinequinone expressed by the formula.