This paper presents a radio-frequency identification (RFID) aquarium sensing system in order to monitor the parameters of the environments in an aquarium. The system includes tags, readers, antennas, impedance matching circuits, and embedded sensors. The RFID tag is powered by the reader through electromagnetic waves produced from the reader. ISO 18000-6C RFID protocol is adopted. The magnetic antenna of the RFID tag is made of a magnetic stripe radiator. An omnidirectional antenna radiation pattern is achieved. An inverted-T matching circuit is also designed. The sensors are embedded in the tags. The parameters of the sensors are sent to the readers. The RFID aquarium sensing system exhibits realtime monitoring functions and provides efficient capability for the management of an aquarium.