  We study the properties of double-$\Lambda$ hypernuclei in the relativistic
mean-field theory, which has been successfully used for the description of
stable and unstable nuclei. With the meson-hyperon couplings determined by the
experimental binding energies of single-$\Lambda$ hypernuclei, we present a
self-consistent calculation of double-$\Lambda$ hypernuclei in the relativistic
mean-field theory, and discuss the influence of hyperons on the nuclear core.
The contribution of two mesons with dominant strange quark components (scalar
$\sigma^*$ and vector $\phi$) to the $\Lambda\Lambda$ binding energy of
double-$\Lambda$ hypernuclei is examined.
