Parametrization of polarized parton distributions

We report the polarized parton distributions proposed by the Asymmetry Analysis Collaboration (AAC). Using parametrized distributions at Q^2=1 GeV^2 and measured A_1 data, we determine optimum polarized distributions in the leading order (LO) and next-to-leading order (NLO). We find that the polarized antiquark distribution is not well determined particularly at small x. It could lead to a rather small quark spin content in comparison with usually-quoted values of 10-30%. In our analysis, it varies from 5% to 28% depending on the small-x extrapolation. It is necessary to have small-x (