A method for transmitting multi-cast packets is provided, including the steps of (a) receiving a plurality of multi-cast packets and generating corresponding port masks to indicate a plurality of ports from which the multi-cast packets are to be transmitted, (b) selecting, based on the yet-enqueued ports indicated in port masks, a port with highest priority, enqueuing the multi-cast packet into the port, and updating the port masks, (c) checking whether the port with highest priority being full-duplex, and (d) determining when to repeat steps (b) to (d) base on the result of the checking, until finishing the transmission specified by the port masks. In step (d), when the port with highest priority is full-duplex, wait until the port with highest priority starting transmitting the packet, then repeat steps (b) to (d). On the other hand, when the port with highest priority is half-duplex, wait until the port with highest priority transmitting a certain portion of the packet, for example 64 bytes or 128 bytes, then repeat steps (b) to (d). This will repeat until finishing all the transmission specified by the port masks. Preferably, the port with highest priority means the port of the highest priority group with the shortest output queue. When finishing all the transmission specified by the port masks, the switch will release all the related buffers of the multi-cast packets.