A communication device for handling a hybrid automatic repeat request (HARQ) transmission comprises a storage unit for storing instructions and a processing circuit coupled to the storage unit. The processing circuit is configured to execute the instructions stored in the storage unit. The instructions comprise performing a first downlink (DL) reception in a first subframe from a serving cell; and transmitting a first HARQ feedback in response to the first DL reception in a second subframe to the serving cell, wherein the second subframe is determined according to the first subframe and a sum of a predetermined timing and a first HARQ timing.