  In supersymmetric axion models, if the gravitino or axino is the lightest
SUSY particle (LSP), the other is often the next-to-LSP (NLSP). We investigate
the cosmology of such a scenario and point out that the lifetime of the NLSP
naturally becomes comparable to the present age of the universe in a viable
parameter region. This is a well-motivated example of the so-called decaying
dark matter model, which is recently considered as an extension of the
$\Lambda$CDM model to relax some cosmological tensions.
