A waste recycling technique using sub- and supercritical water was developed for obtaining useful materials from marine wastes. As a preliminary work, the effect of reaction parameters was investigated using various types of reactors and samples. In order to obtain amino acids effectively, two main reactions (i.e. hydrolysis of proteins to amino acids and decomposition of amino acids) should be considered. The highest amount of amino acids was obtained at 523 K in reaction time of 60 min. The reaction temperature of 523 K was in agreement with the temperature indicating the maximum ion product of water at saturated vapor pressure. At 573 K, the amount of amino acids produced was low since amino acid decomposition rate was higher compared to production of amino acids from protein hydrolysis. Proper control of reaction parameters is necessary in order to obtain high yield of amino acids efficiently. The technique could be useful in establishing a material recycling system across various industries and production processes, with the goal to curtail waste emissions into the environment.