The present disclosure relates to transmission prioritization in wireless communications. According to an embodiment of the present disclosure, a method performed by a wireless device in a wireless communication system comprises: configuring a threshold; creating a media access control (MAC) protocol data unit (MAC PDU) for sidelink comprising a MAC control element (CE); setting a priority value to the MAC CE; identifying a transmission of the MAC PDU for sidelink and an uplink transmission to be performed; determining that the transmission of the MAC PDU for sidelink and the uplink transmission are not able to be performed simultaneously; determining that the priority value of the MAC CE is lower than the threshold; prioritizing the transmission of the MAC PDU for sidelink over the uplink transmission; and performing the transmission of the MAC PDU for sidelink that is prioritized over the UL transmission.