  We study the decay B0->D*+D*-Ks using (230 +/- 2) x 10^{6} BBbar pairs
collected by the Babar detector at the PEP-II B factory. We measure a branching
fraction B(B0->D*+D*-Ks)=(4.4\pm0.4\pm0.7)\times 10^{-3} and find evidence for
the decay B0->D*- D+_{s1}(2536) with a significance of $4.6\sigma$. A
time-dependent CP asymmetry analysis is also performed to study the possible
resonant contributions to B0->D*+D*-Ks and the sign of cos2beta . Our
measurement indicates that there is a sizable resonant contribution to the
decay B0->D*+D*-Ks from a unknown $D^+_{s1}$ state with large width, and that
cos2beta is positive at the 94 % confidence level under certain theoretical
assumptions.
