Radio Frequency Identification (RFID) systems have been used commonly in different areas in the last decades. Identification of animals has been done for a long time by using passive RFID tags and also some digestive system parameters have been monitored trough sensors equipped with active RFID tags. The aim of this study is to develop a bolus that can accurately measure the rumen pH which has higher length of frequency. Three cannulated local breed steers were used for this study. The Hanna 1270 pH sensor was added to the active RFID tags. The buffer (Operational Amplifier) OPAMP was equipped with the pH sensor outputs which were sent to the analogue digital converter. Either the PCB (Printed Circuit Board) helical or a quarter wave monopole antennas connected to a laptop computer were used with UDEA RFID software. The active PCB helical antenna in the active RFID tags was weaker in signaling than a quarter wave monopole antennas. Despite power supply can be extended to nearly a year when it is recorded in 30 minutes intervals, the accuracy of the pH probe is to loss in forty-five days.