The aim of this study was to estimate the time of ovulation and mating derived by plasma progesterone and estradiol-$17{eta}$ concentrations. The 11 pregnant Shih-tzu bitches were investigated the plasma progesterone and estradiol-$17{eta}$ concentrations from proestrus to parturition. Gestation length in the 11 pregnant bitches was $61.9{pm}1.1;(mean{pm}SD)$ days when Day 0 was timed from the day that plasma progesterone concentration was first increased above 4.0 ng/ml. The litter size was $3.8{pm}0.3$ pups. Plasma progesterone concentrations were increased at the first day of vulvar bleeding and showed at Day 0 with $5.2{pm}0.3$ ng/ml. It was gradually increased to reach a peak at Day 15 with $42.6{pm}3.7ng/ml$, thereafter it was gradually decreased to below Day 62. Plasma estradiol-$17{eta}$ concentrations were increased above 1.0 pg/ml at the first day of vulvar bleeding and showed a peak at Day -2 with $33.5{pm}8.0$ pg/ml, thereafter it was gradually decreased. When Day 0 was timed from the day that plasma progesterone concentration was first increased above 4.0 ng/ml, plasma estradiol-$17{eta}$ concentration reached a peak at Day -2. In conclusion, these results indicated that ovulation was estimated to occur the day when plasma progesterone concentration was first increased above 4.0 ng/ml after the first day of bleeding. It was estimated that mating time was the day when plasma progesterone concentration was between $3.0{~}8.0$ ng/ml.