Provided are a Peripheral Component Interconnect Express (PCIe) interface device and a method of operating the same. The PCIe interface device includes a first buffer, a second buffer, and a buffer controller. The first buffer may be configured to store a plurality of first transaction layer packets received from multiple functions. The second buffer may be configured to store a plurality of second transaction layer packets received from the multiple functions. The buffer controller may be configured to, when a first buffer of a switch is full, realign an order in which the plurality of second transaction layer packets are to be output from the second buffer to the switch, based on IDs of the plurality of second transaction layer packets.