Pesin's formula relates the entropy of a dynamical system with its positive Lyapunov exponents. It is well known, that this formula holds true for random dynamical systems on a compact Riemannian manifold with invariant probability measure which is absolutely continuous with respect to the Lebesgue measure. We will show that this formula remains true for random dynamical systems on R d which have an invariant probability measure absolutely continuous to the Lebesgue measure on R d . Finally we will show that a broad class of stochastic flows on R d of a Kunita type satisfies Pesin's formula.