  Nuclear parton distribution functions (NPDFs) are determined by a global
analysis of experimental measurements on structure-function ratios
F_2^A/F_2^{A'} and Drell-Yan cross section ratios
\sigma_{DY}^A/\sigma_{DY}^{A'}, and their uncertainties are estimated by the
Hessian method. The NPDFs are obtained in both leading order (LO) and
next-to-leading order (NLO) of \alpha_s. As a result, valence-quark
distributions are relatively well determined, whereas antiquark distributions
at x>0.2 and gluon distributions in the whole x region have large
uncertainties. The NLO uncertainties are slightly smaller than the LO ones;
however, such a NLO improvement is not as significant as the nucleonic case.
