We observed formation of organic aggregates from a solution of complex organics which were abiotically synthesized from a simulated primitive earth atmosphere with high-energy protons. The structure of the complex organics was partly altered under hydrothermal conditions to form organic aggregates. The aggregates possessed properties of combined amino acids, which had high tolerance against heating. Formation of this kind of organic aggregates might have been an important step in the chemical evolution leading to the origin of life.