α-L-Rhamnosidases cleave terminal nonreducing α-L-rhamnosyl residues from many natural rhamnoglycosides. This makes them catalysts of interest for various biotechnological applications. The X-ray structure of the GH78 family α-L-rhamnosidase from Aspergillus terreus has been determined at 1.38 Å resolution using the sulfur single-wavelength anomalous dispersion phasing method. The protein was isolated from its natural source in the native glycosylated form, and the active site contained a glucose molecule, probably from the growth medium. In addition to its catalytic domain, the α-L-rhamnosidase from A. terreus contains four accessory domains of unknown function. The structural data suggest that two of these accessory domains, E and F, might play a role in stabilizing the aglycon portion of the bound substrate.