  We investigate the enrichment of europium, as a representative of r-process
elements, in the Galactic halo. In present chemical evolution models, stars are
assumed to be formed through shock processes by supernovae (SNe). The
enrichment of the interstellar medium is calculated by a one-zone approach. The
observed large dispersions in [Eu/Fe] for halo stars, converging with
increasing metallicity, can be explained with our models. In addition, the mass
range of SNe for the {\it r}-process site is constrained to be either stars of
$8-10 M_\odot$ or $\gtrsim 30 M_\odot$.
