Homogeneous precipitation of $Y^{3+}$ with urea has been studied in order to investigate the effect of urea concentration on the preparation of monodispersed colloidal "Yttrium Hydroxycarbonate $(Y(OH)CO_3 cdot nH_2O)$". As the initial concentration of urea increased, the mean size of colloidal precipitates decreased, and the rate of precipitation of $Y^{3+}$ increased. When the initial concentration of urea was higher than $4.0 sim 7.0 M$, precipitates obtained were no more monodispersed colloidal particles, but coagulated big particles; and, although the initial concentration of urea increased over 4.0 M, the rate of precipitation did not increased. It is important to decide the proper initial concentration of urea, because excessive urea can cause the environmental problems such as water pollution.