Provided is a glass strengthening method including preparing a glass and strengthening the glass by providing the glass with a molten salt, wherein the molten salt has a freezing point of about 220° C. or more and less than 320° C. In addition, the molten salt includes a first salt and a second salt that are different from each other, wherein the first salt is KNO3, and the second salt includes at least one ion of Li+, Na+, K+, Cs+, and/or Rb+.