I have studied the gauge/gravity correspondence in the background of superstring theory. The important point of the gauge/gravity correspondence is that the strong-coupling Yang-Mills theory that is difficult to analyze can be analyzed by using weak-coupling dual supergravity. In particular, I apply the gauge/gravity correspondence for understanding the difficult physics of a strongly-correlated system and condensed matter physics, such as strongly-correlated electrons. For example, we derived some FQHE and edge states from superstring theory by using the gauge/gravity correspondence.