To provide a specific solution system and a separation method, by which a substance being dissolved, mixed or dispersed in various kinds of solutions can easily be separated.

In the separation method and the solution system, the substance to be extracted is separated by relatively or kinetically changing the mixing ratios of a mixed solution comprising at least three kinds of solutions. The three kinds of solutions satisfy at least following relations: 1. A liquid A and a liquid B mutually dissolve, mix or disperse at an arbitrary ratio. 2. The liquid A and a liquid C mutually dissolve, mix or disperse at an arbitrary ratio. 3. Either of the liquid B and the liquid C dissolves, mixes or disperses in the other liquid in an amount of <10%. The substance to be extracted can be more efficiently separated under following conditions: 4. The substance D to be extracted is able to dissolve, mix or disperse in the liquids A and B in an amount of <5%. 5. The substance D dissolves in the liquid C. The stability of the mixed solution can be improved by using a surfactant.