The reductive tricarboxylic acid (RTCA) cycle is one of the carbon fixation pathways, in which organic compounds are synthesized from carbon dioxide through the reversal flow of the TCA cycle. Because this cycle is presumed to be one of the most ancient pathways for life, studies on the occurrence of this cycle and the characterization of relative metabolism are expected to be of help for better understanding of the origin of life and its evolution. I am planning to reconstruct primitive reactions of the RTCA cycle, reproduce the evolutionary process in which this cycle was established, and explore biochemical clues to identification of metabolism that can support and cooperate with the ancient form of this cycle. The plan will be presented in this seminar.