Washing is an important process for surimi production, in which undesirable components in fish mince are removed, while myofibrillar proteins are concentrated. However, dewatering is less effective for some fish species. The use of appropriate salt can be a means to increase dewatering and simultaneously improve the gelling property of surimi. The impact of 0.45% NaCl containing CaCl₂ or MgCl₂ at various levels (0, 4, 8, 12, 16, and 20 mM) as the third washing media on dewatering of washed mince and gel-forming ability of surimi produced from yellowtail barracuda (Sphyraena flavicauda) was investigated. When CaCl₂ or MgCl₂ was incorporated into the washing media, the contents of Ca or Mg ions in washed mince increased (p < 0.05), whereas the pH of washed mince slightly decreased (p < 0.05). At the same concentration, a higher dewatering of mince was observed when CaCl₂ was used, compared with MgCl₂ (p < 0.05). Differential scanning calorimetry indicated that the stability of myosin decreased when higher concentrations of both salts were used (p < 0.05), while no difference in the stability of actin was obtained. Washing mince with 0.45% NaCl containing 20 mM MgCl₂ yielded increases in breaking force of the gel of resulting surimi for both one-step and two-step heating processes by 46% and 33%, respectively, compared with the control (without CaCl₂ or MgCl₂ incorporation in washing media). The whiteness of the gel slightly decreased when the mince was washed with MgCl₂ (p < 0.05). Microstructure revealed that a gel possessing a fine network with improved water-holding capacity was formed when the third media containing 0.45% NaCl and 20 mM MgCl₂ was used. The use of 0.45% NaCl containing 20 mM MgCl₂ was recommended to increase dewatering efficacy and improve gel strength of surimi from yellowtail barracuda by rendering a fine and ordered gel network.