  We investigate the moduli stabilization in string gas compactification. We
first present a numerical evidence showing the stability of the radion and the
dilaton. To understand this numerical result, we construct the 4-dimensional
effective action by taking into account T-duality. It turns out that the
dilaton is actually marginally stable. When the moduli other than the dilaton
is stabilized at the self-dual point, the potential for the dilaton disappears
and then the dilaton is stabilized due to the hubble damping. In order to
investigate if this mechanism works in more general cases, we analyze the
stability of $T_2 \otimes T_2 \otimes T_2$ compactification in the context of
massless string gas cosmology. We found that the volume moduli, the shape
moduli, and the flux moduli are stabilized at the self dual point in the moduli
space. Thus, it is proved that this simple compactification model is stable.
