  We study the longitudinal polarization of hyperons and anti-hyperons at
forward pseudorapidity, $2.5<\eta<4$, in singly polarized $pp$ collisions at
RHIC energies by using different parameterizations of the polarized parton
densities and different models for the polarized fragmentation functions. The
results show that the $\Sigma^+$ polarization is able to distinguish different
pictures on spin transfer in high energy fragmentation processes; and the
polarization of $\Lambda$ and $\bar\Lambda$ hyperons can provide sensitivity to
the helicity distribution of strange sea quarks. The influence from beam
remnant to hyperon polarization in the forward region is also discussed.
