This paper focuses on the low fertility of Sapporo and considers its demographic features among the designated cities by using Japanese Census and Vital Statistics in 2005. The important findings are as follows. 1. The cluster analysis shows 4 fertility patterns, "Industrial city"," Service industry city", "City with national average fertility" and "City with lowest low fertility" (Sapporo, Tokyo special wards). 2. The factor analysis indicates Sapporo's unique features. The proportion of married women and the marital fertility have almost same weight on low fertility and the catch-up effect realizing postponed marriage and birth by an advanced age does not work. 3. The different net-migration between male and female population causes the lowest sex ratio and the lowest first marriage rate of women in 15 cities at ages 25-29. This results again in the lowest singles sex ratio and the lowest first marriage rate at ages 30-34, so that the catch-up effect doesn't occur. 4. The negative correlation is observed between the mean age of woman at first childbirth and the proportion of the 3rd births in total births.Since the former has highly positive correlations with the mean age at first marriage, the late marriage in Sapporo could cause the late first childbirth and result in giving up to have the 3rd and more children.