We report the first observation of the decay B̄0→Ds+Λ p̄ with a statistical significance of 6.6σ. We measure B(B̄0→Ds+Λp̄)=(2.9±0.7±0.5±0.4) ×10-5, where the first error is statistical, the second is systematic, and the third error comes from the uncertainty in B(Ds+→π+). The data used for this analysis was accumulated at the Υ(4S) resonance, using the Belle detector at the KEKB asymmetric-energy e+e- collider. The integrated luminosity of the data sample is 414fb-1, corresponding to 449×106 BB̄ pairs. © 2007 The American Physical Society.