We explore how the η–π0 mixing angle and the η meson decay into π+π− π0 and 3π0 are modified n the nuclear medium on the basis of the in-medium chiral effective theory with varying isospin asymmetry α, where α ≡ δρ/ρ with δρ = ρn − ρp and ρ = ρn + ρp. We find that the larger the …