  We report an improved measurement of the B+ -> D+ D0bar and B0 -> D0 D0bar
decays based on 657 10^6 BBar events collected with the Belle detector at KEKB.
We measure the branching fraction and charge asymmetry for the B+ -> D+ D0bar
decay: B(B+ -> D+ D0bar)=(3.85 +- 0.31 +- 0.38) 10^{-4} and Acp(B+ -> D+
D0bar)=0.00 +- 0.08 +- 0.02, where the first error is statistical and the
second is systematic. We also set the upper limit for the B0 -> D0 D0bar decay:
B(B0 -> D0 D0bar)< 0.43 10^{-4}at 90% CL.
