The present invention discloses a method for dynamic packet retransmissions of a radio link control, hereinafter called RLC, layer for an RLC entity of a transmitter in a wireless communications system. The method includes the following steps. A first RLC packet, including a first header and a first data field, is transmitted to a receiver. A negative acknowledgment signal corresponding to the first RLC packet is received from the receiver. A first TB size is indicated and received from a protocol layer lower than the RLC layer. A second RLC packet is constructed, whose size depends on the first TB size, includes a second header and a second data field including a portion of the first data field. The second RLC packet is then transmitted to the receiver.