  A next-to-leading order QCD calculation of non-singlet spin structure
function, $g_{1}^{NS} $ is presented within the valon representation of
Hadrons. In the valon model, it is assumed that a nucleon is composed of three
dressed valence quarks: the valons which have their own internal structure, the
valence quark with its associated sea quarks and gluons. The results are in
good agreement with all available data from SMC, E143, HERMES and with the
newly released data from COMPASS experiments. It appears that the small x tail
of $g_{1}^{NS}$ can be described by a single Regge-type exchange. The relevant
parameter of this exchange is given. Finally we show that the polarized proton
structure function has a scaling behavior at small x. The relevant parameters
of this behavior are given too.
