This paper, which is in French with abstracts in both French and English, computes the cohomology ring of orientable and non-orientable Seifert manifolds with \({\mathbb Z}_{p}\) coefficients. The method used is to give an explicit \(\Delta\)-simplicial decomposition of the spaces and to make use of the Alexander-Whitney formula to compute the cup products. The main content of the paper consists of these explicit computations.