A method of QoS rule management with enhanced handling on QoS flow description is proposed. UE checks QoS configuration received from the network for QoS operation errors. When UE receives a QoS rule associated with a specific QFI but has no QoS flow description for the QFI, UE further determines whether the QoS rule is of a GBR QoS flow. If so, UE detects a QoS operation error. If the QoS rule is the default QoS rule, then UE releases the PDU session. If the QoS rule is not the default QoS rule, then UE either rejects a PDU session modification command that carries the QoS rule or deletes the QoS rule carried by a PDU session establishment accept with a 5GSM cause value indicating the QoS operation error.