Bilirubin is glucoronized by uridine diphosphate-glucuronosyl transferase 1A1 (UGT1A1) mainly in the liver, and excreted into bile. The conjugated form is metabolized into the unconjugated form, and then into urobilinogen by bacteria in the intestine. Unconjugated bilirubin and urobilinogen are absorbed into the blood stream. The kidney filtrates conjugated bilurubin and urobilinogen into urine. Accordingly, the reduced enzyme activity of UGTIAI may decrease serum conjugated bilirubin levels, resulting in a lower frequency of positive results of urine bilirubin and urobilinogen. This study examined the associations of UGTIAI Gly71Arg (UGTIAI *6) with urine bilirubin and urobilinogen, as well as serum AST, ALT and GGT. Subjects were 5,172 inhabitants 35 to 69 years old who participated in a cohort study in Nagoya from June 2008 to May 2010. Among them, data from 5,151 participants (1,465 males and 3,686 females) were available for analysis. The age-sex-adjusted odds ratio (OR) of ArgArg relative to GlyGly was 1.37 (95% confidence interval (95% CI), 0.55-1.23) for bilirubin, and 1.67 (95% CI, 0.86-3.26) for urobilinogen. Those of ArgArg+ArgGly were 0.87 (95% CI, 0.59-1.27) and 1.50 (95% CI, 1.17-1.94), respectively. AST, ALT and GGT levels had no associations with the genotype. Although the significant association for urobilinogen was contrary to the biological expectation, this study indicated that UGTIA1 Gly71Arg may be a genetic factor of urine urobilinogen.