Elastic properties of grain boundaries (GBs) influence the macroscopic behavior of materials such as their resistance to deformation but have proved extremely difficult to measure experimentally. Conventional techniques for studying elastic properties of materials can only provide a macroscopic (grains + boundaries) average response. In this work, local strain measurements using geometric phase analysis have been carried out in ultrafine grained copper (UFG) on twin boundaries containing dislocations. Experimental results and simulations using isotropic elasticity reveal an easier deformability of the boundary compared to the matrix. Enrichment of the boundaries in dislocations during deformation seems to eliminate this effect by mutual canceling of the strain fields from adjacent dislocations.