  We analyse the restricted phase space thermodynamics (RPST) of Kerr-Sen-AdS
black holes with the central charge $C$ and its conjugate chemical potential
$\mu$ but exclude the familiar $PdV$ term in the first law of black hole
thermodynamics. That gives rise to a new perspective on the thermodynamics of
black holes. Using the scaling properties, we investigate the first law and the
corresponding Euler formula. Such formalism has its beauty, to say, for
example, the mass is considered to be a homogeneous function of the extensive
variables in the first order. In contrast, the intensive variables are of
zeroth order. Because of the complicated expressions of the metric, we
numerically calculate the critical values of the thermodynamic quantities. We
find the phase transition behaviour of the free energy and other thermodynamic
conjugate variables that appear in the first law. The RPST of the Kerr-Sen-AdS
black holes is like that of the Reissner-Nordstr$\ddot{o}$m-AdS and the
Kerr-AdS black holes. Such notions of the phase transition behaviour show that
there should be some underlying universality in the RPST formalism.
