An alcoholic-aqueous solution of LiBr . H2O is a useful solvent for silk fibroin, if the ratio of alcohol content to water content therein is 1 or more. The mixed solvents consisting of ethanol, water, and LiBr . H2O showed a higher solubility if they contained a lesser amount of water. They further proved able to easily dissolve more than 20% by weight of silk fibroin. Solvents poorer in water content and richer in LiBr . H2O showed a higher value of [eta]; Huggins’ coefficient of said solutions varied within a range 0.5-1.0, the minimum appearing at a water content of about 10% weight. Fibroin molecules remained stable in those solutions. The novel solvents for silk fibroin that have been developed by us are named "MU solvents," by taking the initials in the names of Matumoto/Uejima.