Penaeus japonicus hydrolysates were produced by hot-compressed water treatment at 100 degrees C - 200 degrees C and 30 bar for 10 min. Hydrolysate yield varied from 44.87 +/- 1.74% to 88.55 +/- 2.15% with the maximum yield obtained at 200 degrees C. Hydrolysates showed alkaline pH, which incrementally increased with temperature. Protein, phenolic compounds, and Maillard reaction product were 45.76 +/- 1.27 g/100 g dried mass, 12.47 +/- 0.19 mg trolox/g dried mass, and 4.02 +/- 0.01, respectively, in hydrolysates produced at 200 degrees C. Total and reducing sugar contents were 49.30 +/- 0.11 mg/g and 14.18 +/- 1.23 mg/g dried mass, respectively, in hydrolysates produced at 200 degrees C. P. japonicus hydrolysates showed strong free-radical scavenging capacity and DPPH, ABTS, and FRAP activities of 3.08 +/- 0.04, 26.74 +/- 0.06, and 12.12 +/- 0.50 mg TEAC/g dried mass, respectively. The maximum free and total amino acid contents were found in hydrolysates produced at 175 degrees C; further temperature increment degraded amino acids.