Serial ultrasonographic examinations were performed on 9 Miniature Schnauzer bitches from day 15 of gestation until parturition to determine the ultrasonographic measurement of gestational structures. Ovulation was designated the day that plasma progesterone concentration exceeded 4.0 ng/ml (day 0). Extra-fetal structures were measured from day 17 or 18 to 60. Outer uterine diameter (OUD) increased from 6.50 ± 1.06 mm (Mean ± SD) to 50.89 ± 5.62 mm, inner chorionic cavity diameter (ICCD) increased from 2.10 ± 0.15 mm to 37.15 ± 4.36 mm, and length of placenta (PL) increased from 7.50 ± 1.41 mm to 40.62 ± 3.27 mm. OUD and ICCD were significantly and linearly relative to gestational age especially through day 37, whereas PL was not significantly relative to gestational age. Of the extra-fetal structures, ICCD was the most accurate for estimation of gestational age before day 38 of gestation. Fetal structures increased at a linear rate to parturition. Fetal crown-rump length (CRL)