Natural killer (NK) cells are a crucial component of the innate immune system where they respond rapidly to virally infected and tumourous cells. The activation of NK cells is governed by a large variety of cell surface receptors which transduce activating and inhibitory signals upon recognition of specific target ligands. Clr-b is one such inhibitory ligand from the C-type lectin related (Clr) family. Here, we have solved the X-ray crystal structure of the Clr-b ligand bound to the inhibitory NKR-P1B receptor. Within the structure, Clr-b formed a homo-dimer that surprisingly bound only to a single NKR-P1B monomer. The buried surface area of the receptor-ligand interface was 1450 A2 which was much less than what is observed with the human receptor-ligand homologue. While surface plasmon resonance studies revealed the interaction between soluble forms of the receptor and ligand was extremely weak, NKR-P1B tetramers bound extremely well to NKR-P1B expressed on the cell surface, suggesting the interaction may be modulated by avidity effects or some other unknown factor. Together, these results represent the first structural insight into mode of ligand recognition by murine NKR-P1 receptors, thus broadening our understanding of innate immune receptor function.