An edge card mounting structure includes an edge card, an electrical connector disposed on a circuit board, and a rack that holds the edge card and is inserted into the electrical connector to electrically connect the edge card to the electrical connector. The rack includes a rack body that accommodates the edge card, two bearing plates bilaterally disposed in the rack body, and two adjustment members that are elastically pressable to move the accommodated edge card downwardly into abutment against the bearing plates where the electric contacts of the edge card are kept in contact with the respective contact endpieces of the conducting terminal set of the electrical connector for transmitting high frequency signals.