  We consider a general situation where a charged massive scalar field
$\phi(x)$ at finite temperature interacts with a magnetic flux cosmic string.
We determine a general expression for the Euclidean thermal Green's function of
the massive scalar field and a handy expression for a massless scalar field.
With this result, we evaluate the thermal average $<\phi^{2}(x)>$ and the
thermal average of the energy-momentum tensor of a nonconformal massless scalar
field.
