  The temperature behaviour of the pion width in the hadronic phase is
investigated in the framework of the NJL model. The contribution to the width
from the pion-pion collision is considered with a scalar sigma-meson as an
intermediate state. It is shown that the pion width significantly broadens at
$T>0.1$ GeV. Using the two-step iteration method, suggested by Kadanoff and
Baym, the pion spectral function in a hot pion gas is calculated at different
temperatures.
