To provide a concentrated premixture containing piperazine and at least one alkanolamine for an adsorbent with a freezing point as low as possible.

This premixture for producing an adsorbent for removing acidic gas from fluid streams includes at least one alkanolamine, piperazine and water, and in this case, the premixture has a total amine content of higher than 65 mass% and the molar ratio of water to piperazine in the premixture is 1.6 to 4.8. The premixture is excellent in low freezing point. The premixture is diluted to be an instantaneously usable adsorbent using water and/or the alkanolamine.