Thc K+ scattering cross section with the in-medium virtual pion is evaluated in the lowest-order chiralperturbation theory with the density-dependent pion decay constant and mass. The contribution of nuclear pions to thctotal K+-nucleus cross section is found to be about 5% and 12% when the excess pion numbers per nucleon nπ＝ 0.057and 0.13 are used. The inclusion of the off-mass-shell behavior of the K+π amplitude produced a significant improvementin the K+-nucleus cross section.