In this article, the effect of an external magnetic field on the morphology-dependent resonances (MDRs) of a polymeric dielectric microsphere is investigated. The microsphere is mechanically coupled to a composite polymeric Metglas slab. When an external magnetic field is applied to the slab, it elongates leading to a change in the morphology of the microsphere. This in turn leads to a shift in the excited optical resonances. Experiments are carried out to investigate the effect of an external static and harmonic magnetic field on the MDRs shift. The results show that this configuration can be used as an optical magnetic field sensor or as an optical tuning element. (c) 2013 Wiley Periodicals, Inc.