This paper deals with on-chip antennas integrated on silicon wafers for 2.4GHz RFID applications.Electrical characteristics and radiation characteristics of loop antennas were calculated and simulated.Based on the results from calculations and simulations,an on-chip loop antenna was designed for a RFID tag used in 2.4GHz.This paper also gives some guidelines on the design of on-chip loop antennas.Measured results show that 1.2V power supply and 15uA load current can be obtained from a on-chip rectifier with 25dBm EIRP, with the onchip antenna of 1.8mm ×1.8mm chip.