physical and physiological characteristics of coenzyme PQQ which was purified from culture broth were studied. Purified substance was determined as PQQ・Na_2 based on the spectra of NMR, IR, MS, UV and fluorescence, and the analyses of high-performance liquid chromatography and ion chromatography. This result was confirmed by the crystal structure of PQQ using X-ray diffraction analysis. Molar absorption coefficients are 18,100 M^<-1> cm^<-1> with 233 nm, 21,000 M^<-1> cm^<-1> with 259 nm, and 11,600 M^<-1>cm^<-1> with 322 nm at pH 7.0 and room temperature. This PQQ acts as cofactor of glucose dehydrogenase.