To elucidate the influences on the intestinal fecal flora by antituberuculosis drug rifampicin and the combination with other remedies to tuberuculosis, fecal bilirubinoids were fractionated by IMAI's column chromatography, and identified with photochemical natures of them. Examined cases with lung tuberuculosis were consisted of two groups (A) five cases were administered rifampicin (RFP) only, (B) fifteen cases were given RFP and other antituberuculosis drugs, and (C) five normal subjects as control. The results were as follows: 1) After administration of antituberuculosis drugs, the amount of fecal urobilinogen decreased significantly from 198.44mg to 118.63mg averaged daily. 2) No significant change was observed in the results of liver function tests, that is, serum bilirubin, nonspecific colloid reactions, GOT, GPT, cholesterol, alkaline phosphatase and triglyceride before and after medication. 3) Mesobilirubin and dihydromesobilirubin were identified in each two cases out of group A and group B. Mesobilirubin was detected in two cases out of four using first choice remedies to lung tuberuculosis and a case administered Kanamycin, INH and ethambutol. 4) Absorption maxima of the chloroform fraction colored yellow extracted from the feces of group A were not observed in group C. The yellow pigment did not identified as bilirubinoid or rifampicin and its derivatives with absorption spectra and chemical reactions for the bile pigments. 5) The intermediates of bilirubin to urobilinogen were identified in group A and group B, these results support RFP influences on the intestinal fecal flora from the point of bilirubin metabolism in the intestine.