SD-36 is a potent and efficacious STAT3 PROTAC degrader (Kd=~50 nM), and demonstrates high selectivity over other STAT members. SD-36 also effectively degrades mutated STAT3 proteins in cells and suppresses the transcriptional activity of STAT3 (IC50=10 nM). SD-36 exerts robust anti-tumor activity, and achieves complete and long-lasting tumor regression in mouse tumor models. SD-36 is composed of the STAT3 inhibitor SI-109, a linker, and an analog of Cereblon ligand Lenalidomide for E3 ubiquitin ligase.