The majority of historical masonry bridges were constructed early years and they were not originally designed to carry the extent of loads imposed on them by current vehicular traffic and seismic loads. Therefore, many existing masonry arch bridges can need reassessment and upgrading. In addition to arch elements, the most vulnerable structural elements of masonry arch bridges under transverse seismic loads are the spandrel walls. Spandrel wall failures are local failures, however they affect the serviceability of the bridge considerably. The present paper aims to determine transverse nonlinear seismic performances of the spandrel walls of masonry arch bridges strengthened with different techniques, which are i) take down and rebuilt with tapered section instead of straight section, ii) using transverse tie bars, and iii) covering with a Fabric Reinforced Cementitious Matrix (FRCM) composite. The concrete Damage Plasticity (CDP) material model adjusted to masonry structures for the masonry units, Mohr-Coulomb material model for the backfill, and interface interactions between the backfill, spandrel walls, arch and FRCM units are considered in the 3D finite element model of the bridge. Modal, nonlinear static and seismic responses of the spandrel walls strengthened with the above three different techniques are determined using the finite element method, and the results obtained from the unstrengthened and strengthened models are evaluated and compared with each other. Some recommendations are presented for the strengthening of the spandrel walls in masonry arch bridges.