A mobile communication device for providing QoS of packet transmission is provided. The packet transmission from and to the mobile communication device is performed by repeating a predetermined number of interlaces by a predetermined cycle. In the mobile communication device, a wireless module transmits a first sub-packet of a first packet and a first sub-packet of a second packet to a mobile communication network, and receives a response message corresponding to the first sub-packet of the first packet from the mobile communication network, wherein the first sub-packet of the first packet is transmitted in a first interlace prior to a second interlace in which the first sub-packet of the second packet is transmitted. Also, a controller module calculates a plurality of QoS parameters for a second sub-packet of the second packet in response to the response message, prepares the second sub-packet of the second packet with the QoS parameters, and transmits the second sub-packet of the second packet in the second interlace to the mobile communication network via the wireless module.