  We study thermodynamics in $f(R)$ gravity with the disformal transformation.
The transformation applied to the matter Lagrangian has the form of $\g_{\m\n}
= A(\phi,X)g_{\m\n} + B(\phi,X)\pa_\m\f\pa_\n\f$ with the assumption of the
Minkowski matter metric $\g_{\m\n} = \e_{\m\n}$, where $\phi$ is the disformal
scalar and $X$ is the corresponding kinetic term of $\phi$. We verify the
generalized first and second laws of thermodynamics in this disformal type of
$f(R)$ gravity in the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) universe.
In addition, we show that the Hubble parameter contains the disformally induced
terms, which define the effectively varying equations of state for matter.
