  We derive a quantum kinetic theory for QED based on Kadanoff-Baym equations
for Wigner functions. By assuming parity invariance and considering a complete
set of self-energy diagrams, we find the resulting kinetic theory expanded to
lowest order in $\hbar$ generalizes the well-known classical kinetic theory to
massive case. It contains elastic and inelastic collision terms and integrates
screening effect naturally. For a given solution to the classical kinetic
theory, we find at next order in $\hbar$ a non-dynamical quantum correction to
Wigner functions for both fermions and photons, which gives rise to spin
polarization for fermion and photon respectively. The approach allows us to
study the non-dynamical part of collisional effect on spin polarization
phenomenon.
