  Using the closed-time-path formalism, we construct perturbative frameworks,
in terms of quasiparticle picture, for studying quasiuniform relativistic
quantum field systems near equilibrium and non-equilibrium quasistationary
systems. We employ the derivative expansion and take in up to the second-order
term, i.e., one-order higher than the gradient approximation. After
constructing self-energy resummed propagator, we formulated two kind of
mutually equivalent perturbative frameworks: The first one is formulated on the
basis of the ``bare'' number density function, and the second one is formulated
on the basis of ``physical'' number density function. In the course of
construction of the second framework, the generalized Boltzmann equations
directly come out, which describe the evolution of the system.
