Abstract: The present invention provides a process for producing oxazopyrroloquinolines which comprises culturing microorganisms to produce pyrroloquinolinequinone and adding .alpha.-amino acids or monomethylamine to the resulting culture broth which contains the pyrroloquinolinequinone and from which cells of microorganisms are not separated, thereby to convert the pyrroloquinolinequinone to the corresponding oxazopyrroloquinolines.The thus obtained oxazopyrroloquinolines include novel compounds.The present invention further provides aldose reductase inhibitors, diabetic combined disease curing agents, immunopotentiating agents and liver disease inhibiting agents which contain as active ingredient these oxazopyrroloquinolines having excellent physiological activity.