Soluble single-domain fragments derived from the unique variable region of camelid heavy-chain antibodies (VHHs) against enzymes may behave as potent inhibitors. The immunization of alpacas with the CMY-2 β-lactamase led to the isolation of three VHHs that specifically recognized and inhibited CMY-2. The structure of the complex VHH cAbCMY-2(254)/CMY-2 was determined by X-ray crystallography. We showed that the epitope is close to the active site and that the CDR3 of the VHH protrudes in the catalytic site. The β-lactamase inhibition was found to follow a mixed profile with a predominant non-competitive component. The three isolated VHHs recognized overlapping epitopes since they behaved as competitive binder. Our study identified a binding site that can be targeted by a new class of β-lactamase's inhibitors designed with the help of a peptidomimetic approach. Furthermore, the use of mono or bivalent VHH and rabbit polyclonal anti-CMY-2 antibodies enable the development of the first generation of ELISA test for the detection of CMY-2 produced by resistant bacteria.