  Kaon electroweak properties in symmetric nuclear matter are studied in the
Nambu--Jona-Lasinio model using the proper-time regularization. The valence
quark properties in symmetric nuclear matter are calculated in the quark-meson
coupling model, and they are used as inputs for studying the in-medium kaon
properties in the NJL model. We evaluate the kaon decay constant, kaon-quark
coupling constant, and $K^+$ electromagnetic form factor by two different
approaches. Namely, by two different ways of calculating the in-medium
constituent quark masses of the light quarks. We predict that, in both
approaches, the kaon decay constant and kaon-quark coupling constant decrease
as nuclear density increases, while the $K^+$ charge radius increases by
20-25\% at normal nuclear density.
