  We present evidence for the decay B0->rho0 K0s. The results are obtained from
a data sample of 227 10^6 Y(4S) -> BBbar decays collected with the BABAR
detector at the PEP-II asymmetric-energy B-Factory at SLAC. From a
maximum-likelihood fit giving a yield of 99+/-19 events and efficiency
estimated from simulation we make a preliminary measurement of the branching
fraction B0->rho0 K0 =(5.1+/-1.0+/-1.2)10^-6 where the first error is
statistical and the second systematic. The hypothesis of zero signal in the
rho0 mass region, 600MeV-930MeV, is excluded at the 6.1sigma level. Allowing a
B0->f_0(600)K0s contribution in the fit allows us to exclude the hypothesis of
zero B0->rho0 K0s at the 3.5sigma level.
