A communication device for handling channel access in an unlicensed band, comprising: a storage device for storing instructions; and a processing circuit, coupled to the storage unit, wherein the storage unit stores, and the processing circuit is configured to execute, the instructions of: initiating a first channel access procedure according to a first channel access priority class for at least one first packet which is scheduled to be transmitted in a first duration on a carrier in an unlicensed band; setting a first counter, in the first channel access procedure, to a first value according to the first channel access priority class; initiating a second channel access procedure according to a second channel access priority class for at least one second packet which is scheduled to be transmitted on the carrier, while running the first channel access procedure; setting a second counter, in the second channel access procedure, to a second value according to the second channel access priority class, wherein the first value for the first channel access priority class is different than the second value for the second channel access priority class; characterised by transmitting the at least one second packet in a second duration on a first frequency resource on the carrier, when the first counter is not decreased to a first predetermined value and the second counter is decreased to a second predetermined value; and transmitting the at least one first packet in the first duration on a second frequency resource on the carrier, when the first counter is decreased to the first predetermined value and the second counter is not decreased to the second predetermined value. a storage device for storing instructions; and a processing circuit, coupled to the storage unit, wherein the storage unit stores, and the processing circuit is configured to execute, the instructions of: initiating a first channel access procedure according to a first channel access priority class for at least one first packet which is scheduled to be transmitted in a first duration on a carrier in an unlicensed band; setting a first counter, in the first channel access procedure, to a first value according to the first channel access priority class; initiating a second channel access procedure according to a second channel access priority class for at least one second packet which is scheduled to be transmitted on the carrier, while running the first channel access procedure; setting a second counter, in the second channel access procedure, to a second value according to the second channel access priority class, wherein the first value for the first channel access priority class is different than the second value for the second channel access priority class; characterised by transmitting the at least one second packet in a second duration on a first frequency resource on the carrier, when the first counter is not decreased to a first predetermined value and the second counter is decreased to a second predetermined value; and transmitting the at least one first packet in the first duration on a second frequency resource on the carrier, when the first counter is decreased to the first predetermined value and the second counter is not decreased to the second predetermined value. initiating a first channel access procedure according to a first channel access priority class for at least one first packet which is scheduled to be transmitted in a first duration on a carrier in an unlicensed band; setting a first counter, in the first channel access procedure, to a first value according to the first channel access priority class; initiating a second channel access procedure according to a second channel access priority class for at least one second packet which is scheduled to be transmitted on the carrier, while running the first channel access procedure; setting a second counter, in the second channel access procedure, to a second value according to the second channel access priority class, wherein the first value for the first channel access priority class is different than the second value for the second channel access priority class; characterised by transmitting the at least one second packet in a second duration on a first frequency resource on the carrier, when the first counter is not decreased to a first predetermined value and the second counter is decreased to a second predetermined value; and transmitting the at least one first packet in the first duration on a second frequency resource on the carrier, when the first counter is decreased to the first predetermined value and the second counter is not decreased to the second predetermined value.