We report the first observation of the decays B0→pΛ¯D(∗)-. The data sample of 711 fb-1 used in this analysis corresponds to 772×106 BB¯ pairs, collected at the (4S) resonance by the Belle detector at the KEKB asymmetric-energy e+e- collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions of B0→pΛ¯D- and B0→pΛ¯D∗- to be (25.1±2.6±3.5)×10-6 and (33.6±6.3±4.4)×10-6, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the dibaryon (pΛ¯) system is observed, consistent with that observed in similar B decays.