We report results of ab initio calculation of the spin-rotational Hamiltonian parameters including [Formula Presented]- and [Formula Presented]-odd terms for the BaF molecule. The ground-state wave function of BaF molecule is found with the help of the relativistic effective core potential method followed by the restoration of molecular four-component spinors in the core region of barium in the framework of a nonvariational procedure. Core polarization effects are included with the help of the atomic many-body perturbation theory for the Barium atom. For the hyperfine constants the accuracy of this method is about 5–10 %.