Ureaplasma urealyticum (U. urealyticum) and Mycoplasma hominis (M. hominis) are known to cause an intrauterine infection for preterm deliveries, but it is not known whether they are actually pathogenically involved in the development of funisitis, chorioamnionitis (CAM), and chronic lung disease (CLD) in preterm infants. Our purpose was to identify U. urealyticum and M. hominis in the umbilical cord, placenta, and tracheal aspirate (TA) or gastric fluid (GF) of preterm infants, and to clarify whether they contribute to funisitis, CAM, and CLD. Of 128 preterm infants, 86 umbilical cords, 83 placentas, and 84 TA or GF samples obtained postnatally from preterm infants were examined. U. urealyticum and M. hominis were detected by polymerase chain reaction and prospectively analyzed to determine whether the presence of U. urealyticum or M. hominis can lead to the development of funisitis, CAM, and CLD. U. urealyticum or M. hominis was isolated in nine (10.5%) of the umbilical cords, five (6.0%) of the placentas, and fifteen (17.9%) of the TA or GF samples. Funisitis was identified in all umbilical cords with U. urealyticum or M. hominis, but in only 13% of the umbilical cords without U. urealyticum and M. hominis (p < 0.001). Placentas and TA or GF with or without U. urealyticum and M. hominis did not show significant differences with regard to the development of CAM or CLD. Our results suggest that U. urealyticum and M. hominis presence is associated with the pathogenesis of funisitis, but not of CAM or CLD.