The critical parameters of molecular fluids with different molecular shapes and intermolecular potentials have been determined for the purpose of extending the applicability of the RISM-1 type equation obtained by combining a reference interaction site model with the Percus-Yevick approximation. The critical point was taken as the point at which (aP/a(e))(T) = (a(2)P/e(2))(T) = 0, and this point was determined by an extrapolation procedure. The factors examined are the shapes of the molecules (monatomic, diatomic, linear triatomic, and linear tetra-atomic), dihedral angles for homonuclear tetra-atomic molecules, and the repulsive index n of the Lennard-Jones potentials.