Friction Stir Layer Deposition on a Cu-containing high-entropy alloy (HEA) has been performed for its suitability of the core component of nuclear materials. Excellent irradiation resistance in this Cu-containing HEA has been reported previously. Friction stir layer deposition (FSLD) offers a solid-state deformation processing route to metal additive manufacturing, in which the feed material undergoes severe plastic deformation at elevated temperatures. Some of the key advantages of this process are fabrication of fully dense material with fine, equiaxed grain structures. This work reports the detailed microstructure of the FSLD product, and it discusses the grain refinement and micro-hardness variation observed in FSLD product.