We discuss thermodynamics of N M2- and M5-branes by using the method proposed by Smilga and Wiseman, which explains the black Dp-brane thermodynamics from the maximally supersymmetric U(N) Yang-Mills theories. As result we obtain the consistent results with the predictions from the eleven-dimensional supergravity by very simple calculations: The free energy of M2-branes is evaluated by using ABJM theory as F ~ N^{3/2}k^{1/2}T^3, and that of M5-branes is estimated by assuming some natural properties of 6d conformal field theory as F ~ N^3T^6.