A mounting assembly includes a circuit board, a securing member and a heat dissipating device. A retainer is located on the circuit board. The securing member includes a positioning portion and a claw connected to the positioning portion. The heat dissipating device includes a base attached to the circuit board and a number of fins perpendicularly located on the base. The number of fins defines a number of first air paths and a number of second air paths substantially perpendicular to the number of first air paths. The positioning portion is received in at least one of the number of first air paths and at least one of the number of second air paths, and the claw is engaged with the retainer.