The present invention provides a composition for adjusting biological tissue size and a method for adjusting the size of biological tissue using the said composition. The composition for adjusting the size of biological tissue according to the present invention can adjust the size of biological tissue according to the specifications of a microscope and the needs of a researcher, and can be used as a mounting solution to easily acquire an image of the biological tissue. Therefore, the composition can be usefully used to reveal the causes of and find treatment methods for various disorders.