We present a study of the decays B0→Ds(*)+D*-, using 20.8 fb-1 of e +e- annihilation data recorded with the BABAR detector. The analysis is conducted with a partial reconstniction technique, in which only the Ds(*)+ and the soft pion from the D*- decay are reconstructed. We measure the branching fractions B(B0→Ds+D*-) = (1.03±0.14±0.13±0.26)% and B(B0→D* s+D*-) = (1.97±0.15±0. 30±0.49)%, where the first error is statistical, the second is systematic, and the third is the error due to the Ds+ → φπ+ branching fraction uncertainty. From the B 0→D*s+D*- angular distributions, we measure the fraction of longitudinal polarization ΓL/Γ = (51.9±5.0±2.8)%, which is consistent with theoretical predictions based on factorization. © 2003 The American Physical Society.