In this study, we evaluated the effects of osmotic dehydration sheets (ODSs) on quality parameters and morphological observation of tuna stored at 4C for 4 days. The use of ODSs did not affect Hunter L* and b* values, although use of low performance ODSs (ODS-L) gave higher a* values and lower metmyoglobin percentage (Met-Mb%) than other samples (P < 0.05). As increasingly higher-performance ODSs were used, the total sample content of ATP-related compounds and IMP (a component of umami) increased and the K values decreased (P < 0.05), indicating maintenance of tuna freshness. However, Hunter color values and Met-Mb% revealed that the optimum dehydration level exists at low dehydration performance. ODS was effective in removing intercellular water of thawed tuna tissue. We therefore suggest ODS-L as a functional tool for maintaining the color of tuna, and high performance ODS as a functional tool for maintaining freshness and reform watery texture of chilled stored tuna.