A ringtone assignment system and method are provided. The method includes steps of recording a multimedia ringtone via a first communication device, transmitting a communication linking request to a communication exchange host, transmitting the communication linking request to a second communication device via the communication exchange host to enable the second communication device to feed back ringtone format information supported by the second communication device according to the communication linking request, transmitting the ringtone format information to the first communication device via the communication exchange host to enable the first communication device to code the multimedia ringtone according to the ringtone format information, transmitting the multimedia ringtone from the first communication device to the second communication device, and then decoding and playing the multimedia ringtone by the second communication device. The second communication device is able to recode and assign the multimedia ringtone to the first communication device.