  We study the polarization of hyperon in different processes in singly
polarized $pp$ collisions, in particular its relation to the polarized parton
distributions. We show that by measuring hyperon polarization in particularly
chosen processes, one can extract useful information on these parton
distributions. We show in particular that, by measuring the $\Sigma^+$
polarization in high $p_T$ direct photon production process, one can extract
information on the gluon helicity distribution; and by measuring the transverse
polarization of hyeprons with high $p_T$ in singly polarized reactions, one can
obtain useful information on the transversity distribution. We present the
numerical results obtained for those hyperon polarizations using different
models for parton distribution function and those for the spin transfer in
fragmentation processes.
