The mechanism responsible for the deconjugation of the glucuronide of p-phenyl benzoic acid (PPBA) in fetal intestine and amniotic fluid was studied in rats. Non-enzymatic hydrolysis of PPBA glucuronide in intestine was little before birth. The activity of β-glucuronidase (β-G) in fetus was the highest in intestine, followed by lung and skin. The activity of β-G in fetal intestine increased with the day of gestation, and increased remarkably between the 18th and 21st day of gestation. PPBA glucuronide injected intraamniotically distributed as PPBA in fetal skin. The fluid of trachea and esophagus showed high distribution of radioactivity and the ratio of PPBA glucuronide in radioactive substances in fetal lung tended to be higher than that in fetal plasma after intraamniotic injection of ¹⁴C-PPBA glucuronide. In summary, PPBA glucuronide in amniotic fluid is absorbed into fetal body through skin, lung and intestine after deconjugation.