  We study the effect of a finite quark mass on the quark number susceptibility
in the framework of holographic QCD. We work in a bottom-up model with a
deformed AdS black hole and D3/D7 model to calculate the quark number
susceptibility at finite temperature with/without a finite quark chemical
potential. As expected the finite quark mass suppresses the quark number
susceptibility. We find that at high temperatures $T\ge 600$ MeV the quark
number susceptibility of light quarks and heavy quarks are almost equal in the
bottom-up model. This indicates that the heavy quark like charm contribution to
thermodynamics of a QCD-like system may start to become significant at
temperatures $T\sim 600$ MeV. In D3/D7 model, we focus on the competition
between the quark chemical potential, which enhances the quark number
susceptibility, and the quark mass that suppresses the susceptibility. We
observe that depending on the relative values of the quark mass and the quark
chemical potential, the quark number susceptibility shows a diverging or
converging behavior. We also calculate the chiral susceptibility in D3/D7 model
to support the observation made with the quark number susceptibility.
