Chalcogenide glasses of As2Se3−xTex (O<x<3) were made with special care, using very pure raw materials in order to avoid traces of oxygen. From these materials optical fibers were pulled, and the attenuation of CO2 laser light (wavelength λ = 10.6 μm) transmitted through these fibers was measured as a function of the Te content (x). The fiber's surface and cross-section were examined, using both the scanning electron and optical microscopes, and they directly revealed the increase in the concentration of the defects while x was increasing. The influence of the physical and mechanical properties on the concentration of defects was studied by measuring the optical absorption (α) and the microhardness (VH) of the raw materials. Slabs of As2Se3−xTex were made, and in these samples the α, VH, and glass transition temperature (Tg) as a function of x were measured. In the infrared region of the spectra at λ = 10.6 μm, the α in both the slabs and pulled fibers increased, and the VH and Tg decreased with the increase of x. This can be explained by the increase of the concentration of the defects (small crystallites) which appeared during the fiber pulling.