  We calculate the partonic structure of constituent quark in the
Next-to-Leading Order for the first time. The structure of any hadron can be
obtained thereafter using a convolution method. Such a procedure is used to
generate the structure function of proton and pion in NLO. It is shown that
while the constituent quark structure is generated purely perturbatively and
accounts to most part of the hadronic structure, there is a few percent
contributions coming from the nonperturbative sector in the hadronic structure.
This contribution plays the key role in explaining the SU(2) symmetry breaking
of the nucleon sea and the observed violation of Gottfried sum rule. These
effects are calculated. Excellent agreement with data in a wide range of
$x=[10^{-6}, 1]$ and $Q^{2}=[0.5, 5000]$ $GeV^{2}$ is reached for proton
structure function. We have also calculated Pion structure and compared it with
the existing data. Again nice agreement is achieved.
