  We investigate the thermodynamic properties of inner and outer horizons in
the background of spinning BTZ(Ba\~{n}ados,Teitelboim and Zanelli) black hole.
We compute the \emph{horizon radii product, the entropy product, the surface
temperature product, the Komar energy product and the specific heat product}
for both the horizons. We observe that the entropy product is
\emph{universal}(mass-independent), whereas the surface temperature product,
Komar energy product and specific heat product are \emph{not universal} because
they all depends on mass parameter. We also show that the \emph{First law} of
black hole thermodynamics and \emph {Smarr-Gibbs-Duhem } relations hold for
inner horizon as well as outer horizon. The Christodoulou-Ruffini mass formula
is derived for both the horizons. We further study the \emph{stability} of such
black hole by computing the specific heat for both the horizons. It has been
observed that under certain condition the black hole possesses \emph{second
order phase transition}.
