© 2015 CERN. © 2015 CERN, for the LHCb Collaboration. Published by the American Physical Society under the terms of the «http://creativecommons.org/licenses/by/3.0/» Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. A search is presented for hidden-sector bosons, χ, produced in the decay B0→K∗(892)0χ, with K∗(892)0→K+π- and χ→μ+μ-. The search is performed using pp-collision data corresponding to 3.0fb-1 collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350MeV, and upper limits are placed on the branching fraction product B(B0→K∗(892)0χ)×B(χ→μ+μ-) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10-9 for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.