The first observation of the decay B0
s → D0K∗0 using pp data collected by the LHCb detector at a centreof-mass
energy of 7 TeV, corresponding to an integrated luminosity of 36 pb−1, is reported. A signal
of 34.4 ± 6.8 events is obtained and the absence of signal is rejected with a statistical significance of
more than nine standard deviations. The B0
s → D0K∗0 branching fraction is measured relative to that of
B0 → D0ρ0: B(B0
s →D0 K∗0)
B(B0→D0ρ0) = 1.48±0.34±0.15±0.12, where the first uncertainty is statistical, the second
systematic and the third is due to the uncertainty on the ratio of the B0 and B0
s hadronisation fractions