A multi-serial port connection device has a connection card and a cable. The connection card has a serial signal transceiving control module and at least one Mini DisplayPort connector. The serial signal transceiving control module has at least two sets of serial I/O pins compatible with DB9 connector standard. The two sets of serial I/O pins are connected to twenty contacts of the Mini Display Port connector. The cable has a plug, at least two DB9 sockets for the connection of two external electronic devices with DB9 connectors. The multi-serial port connection device can reduce the space occupied by connectors on the connection card.