Grain boundary sliding is an important deformation mechanism that contributes to creep and superplastic forming. In tin-based lead-free solders grain boundary sliding can make significant contributions to in service performance. Novel microcompression tests designed to isolate individual grain boundaries and assess their mechanical resistance to sliding were conducted on tin. The boundary sliding deformation was more obvious for smaller sample cross-sections and made a larger contribution to the overall deformation. As with dislocation and twinning mediated plasticity there was a significant size effect in which the resistance to grain boundary sliding increases as the sample size is reduced. The two Excel files contain: 1. stress-displacement curves from compression tests made on micro-pillars of different sizes cut in the bi-crystal and the two constituent single crystals. 2. flow stress versus pillar size for the bi-crystal and the two constituent single crystals, along with the percentage of total deformation contributed by grain boundary sliding in the bi-crystal test pieces as a function of size.