  We study parametrization of polarized parton distribution functions in the
\alpha_s leading order (LO) and in the next-to-leading order (NLO). From \chi^2
fitting to the experimental data on A_1, optimum polarized distribution
functions are determined. The quark spin content \Delta\Sigma is very sensitive
to the small-x behavior of antiquark distributions which suggests that small-x
data are needed for precise determination of \Delta\Sigma. We propose three
sets of distributions and also provide FORTRAN library for our distributions.
