  We study primordial tensor power-spectra generated during inflation in
bimetric gravity. More precisely, we examine a homogeneous expanding spacetime
in a minimal bimetric model with an inflaton and calculate tensor perturbations
on the homogeneous background under slow-roll approximation. In terms of the
mass eigenstates, only the power-spectrum of the massless state remains
constant and both the power-spectrum of the massive state and the cross
power-spectrum rapidly decay during inflation. The amplitude of the physical
power-spectrum is suppressed due to the flavor mixing. All power-spectra in the
flavor eigenstates coincide with each other up to the first order of the
slow-roll parameter.
