This paper presents a novel structure and method for modeling and digitally pre-distorting outphasing amplifiers. The models and pre-distortion are evaluated on a CMOS low-power class-D outphasing amplifier using uplink WCDMA signals. Using the proposed pre-distorter improves the ACLR by no less than 12 dB making the amplifier fulfill the 3GPP requirements on ACLR.