A high-PSR capless-LDO circuit with body-ripple injection based on 40 nm CMOS IC process was designed. The circuit is powered by a 1.1 V power supply, and the LDO output voltage is stable at 0.9 V. Simulation results show that the PSR of conventional capless-LDO circuit increases to a peak at the UGF of the loop and then begin to decrease through the capacitor-to-ground path at the output node. The highest PSR is even greater than 0 dB. The LDO using the new substrate ripple injection technology can adequately suppress the PSR peak and achieve the entire frequency band above -20 dB. Compared with the conventional structure, the PSR at the peak increases by more than 20 dB. The LDO can be applied to RF circuits that require low voltage power supplies.