  In this paper, we investigate one-loop radiative corrections to the Casimir
energy in the presence of two perfectly conducting parallel plates for QED
theory within the renormalized perturbation theory. In fact, there are three
contributions for radiative corrections to the Casimir energy, up to order
$\alpha$. Only the two-loop diagram, which is of order $\alpha$, has been
computed by Bordag et. al (1985), approximately. Here, up to this order, we
consider corrections due to two one-loop terms, i.e., photonic and fermionic
loop corrections resulting from renormalized QED Lagrangian, more precisely.
Our results show that only the fermionic loop has a very minor correction and
the correction of photonic loop vanishes.
