We investigate the strain in core-shell nanowires consisting of a highly mismatched materials system of a GaAs core and a MnAs shell. The strain in the GaAs core is directly traced using Raman spectroscopy, whereas that in the MnAs shell is assessed by magnetization measurements. The Raman peak positions in the MnAs-capped nanowires are shifted in comparison to those in bare GaAs nanowires in a nonuniform manner. We theoretically explore the influence of the anisotropic strain in the core-shell nanowires on the peak shift. When the shell thickness considerably exceeds the core diameter, the shell is only weakly strained. This can be interpreted as the shell taking over the role of the rigid substrate. In addition, we evaluate the diffusion length in the MnAs growth. (C) 2010 Elsevier B.V. All rights reserved.