In the present study, the human TEB4 is identified as a novel ER (endoplasmic reticulum)-resident ubiquitin ligase. TEB4 has homologues in many species and has a number of remarkable properties. TEB4 contains a conserved RING (really interesting new gene) finger and 13 predicted transmembrane domains. The RING finger of TEB4 and its homologues is situated at the N-terminus and has the unconventional C4HC3 configuration. The N-terminus of TEB4 is located in the cytosol. We show that the isolated TEB4 RING domain catalyses ubiquitin ligation in vitro in a reaction that is ubiquitin Lys48-specific and involves UBC7 (ubiquitin-conjugating enzyme 7). These properties are reminiscent of E3 enzymes, which are involved in ER-associated protein degradation. TEB4 is an ER degradation substrate itself, promoting its own degradation in a RING finger- and proteasome-dependent manner.