Chalcogenide glasses are known for their large transparency in the mid infrared, which includes the two atmospheric windows lying from 3-5 μm and 8-12 μm. Chalcogenide single mode fibers present numerous potential applications in the IR field, such as military countermeasures, LIDAR spectroscopy and spatial interferometry. Two routes can be considered for the elaboration of a single mode fiber. The first method consists in preparing a classical step index fiber (SIF) with a core-clad configuration. This procedure is based on two glass compositions (core and clad) with compatible thermal and optical properties and having a refractive index difference allowing the single mode propagation. The second route is based on the design of a microstructured optical fiber (MOF) in which the guiding function is ensured by the refractive index contrast between the core glass and the air contained in the capillaries surrounding the core. Two kinds of fibers exhibiting single mode propagation were fabricated; the first one is a SIF with a 22 μm core diameter and the second one is a three rings of holes MOF. The geometry of the MOF shows a d/Λ around 0.35 and a 40 μm core diameter. In both cases the optical losses in the 2 to 12 μm region were measured and compared.