To provide a packaging structure of an electronic part capable of effectively filling gaps between electronic parts flip-chip mounted on both the surfaces of a circuit board and the circuit board with underfill, and its packaging method.

In the structure, gaps 6 and 8 between a circuit board 3 and semiconductor chips 1 and 2, which are individually flip-chip mounted on both the surfaces of the circuit board, 3 are filled with underfill 7 in a state where the underfill 7 of the semiconductor chip 1 and the underfill 7 of the semiconductor chip 2 communicate each other via a perforated hole 9 provided into the circuit board 3. When one open end 9a of the perforated hole 9 locates near the gap 6, and the other open end 9b locates in the gap 8, the gaps can be filled with liquefied underfill 70 by pouring the underfill 70 into the gap 6 from the lateral side near the open end 9a and pouring the underfill 70 into the gap 8 via the perforated hole 9.