A portable computer and a hinge mechanism thereof are provided. The portable computer includes a display monitor, a host and a hinge mechanism. The hinge mechanism for rotating the display monitor and the host relatively includes a bottom board, a pivot, a power adapter, a locking bracket, a slanting board and a parallel board. The pivot is disposed on the bottom board. Two ends of the pivot are connected with the host and the display monitor respectively. The power adapter is disposed on the bottom board. The locking bracket having a locking hole is disposed on the bottom board. The slanting board disposed on the bottom board slants to the pivot. The slanting board has a first opening which exposes the power adapter. The parallel board disposed on the bottom board is parallel to the pivot. The parallel board has a second opening which exposes the locking hole.