The aim of this work was to study the effect of austenitic grain size (GS) reduction on the structural parameters of the epsilonhcp - martensite in stainless shape memory alloy (SMA). Rietveld refinement data showed an expansion in c-axis and a reduction in a and b-axis with thermo-mechanical cycles for all samples analyzed. Samples with 75 < GS (µm) < 129 were analyzed. It was also observed an increase of the unit cell volume in this phase with GS reduction. The smallest grain size sample (GS = 75 µm) presented a c/a ratio of 1.649, and approximately 90% of total shape memory recovery.6367Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)