Let f = (f 1 ,. .. , f s) be a sequence of polynomials in Q[X 1 ,. .. , X n ] of maximal degree D and V ⊂ C n be the algebraic set defined by f and r be its dimension. The real radical re f associated to f is the largest ideal which defines the real trace of V. When V is smooth, we show that re f , has a finite set of generators with degrees bounded by deg V. Moreover, we present a probabilistic algorithm of complexity (snD n) O(1) to compute the minimal primes of re f. When V is not smooth, we give a probabilistic algorithm of complexity s O(1) (nD) O(nr2 r) to compute rational parametrizations for all irreducible components of the real algebraic set V ∩ R n. Experiments are given to show the efficiency of our approaches.