Katanin is a microtubule-severing enzyme that is crucial for many cellular processes. Katanin consists of two subunits, p60 and p80, that form a stable complex. The interaction between subunits is mediated by the p60 N-terminal microtubule-interacting and -trafficking domain (p60-MIT) and the p80 C-terminal domain (p80-CTD). Here, we performed a biophysical characterization of the mouse p60-MIT:p80-CTD heterodimer and show that this complex can assemble into heterotetramers. We identified two mutations that enhance heterotetramer formation and determined the X-ray crystal structure of this mutant complex. The structure revealed a domain-swapped heterotetramer consisting of two p60-MIT:p80-CTD heterodimers. Structure-based sequence alignments suggest that heterotetramerization of katanin might be a common feature of various species. Furthermore, we show that enhanced heterotetramerization of katanin impairs its microtubule end-binding properties and increases the enzyme's microtubule lattice binding and severing activities. Therefore, our findings suggest the existence of different katanin oligomers that possess distinct functional properties.