  The charge form factor and weak decay constant of the pion as well as the
pion-quark coupling constant in symmetric nuclear matter are explored in the
framework of the Nambu--Jona-Lasinio model, where the pion is described as a
bound state of dressed quark-antiquark pair obtained by the Bethe-Salpeter
equation. For the in-medium current quark properties, we adopt the quark-meson
coupling model, which describes successfully many hadron properties in a
nuclear medium. The pion decay constant and the pion-quark coupling constant
are found to decrease with increasing density as well as the magnitude of the
light quark condensate. But the pion mass is found to be insensitive to density
up to $1.25$ times the normal nuclear density. The pion charge form factor in
the space-like region is also explored and is found to have a similar $Q^2$
dependence as the form factor in vacuum showing $1/Q^2$-behavior in large $Q^2$
region, where $Q^2$ is the negative of the four-momentum transfer squared. The
modifications of the charge radius of the charged pion in nuclear matter are
then estimated and the root-mean-square radius at the normal nuclear density is
predicted to be larger than that in vacuum by about 20\%.
