  We perform the analysis of the existing inclusive deep inelastic scattering
(DIS) data within NNLO QCD approximation. The parton distributions functions
(PDFs) and the value of strong coupling constant
$\alpha_{s}(M_Z)=0.1143\pm0.0013 (exp)$ are obtained. The sensitivity of the
PDFs to the uncertainty in the value of the NNLO corrections to the splitting
functions is analyzed. It is shown that the PDFs errors due to this uncertainty
is generally less than the experimental uncertainty in PDFs through the region
of $x$ spanned by the existing DIS data.
