Transmission Electron Microscopy is an essential technique for imaging the microstructures at the nanometer scale. However, quantitative analysis of such images is not easy due to the nature of TEM contrast based on diffraction phenomena. A quantitative description of the microstructure of melt-spun AIY ribbons has been carried out in the present work. TEM observations have revealed randomly distributed and oriented spherical nanometer crystals. ln order to describe quantitatively their size and shape, images under different diffraction conditions were recorded. These images have been analyzed using software for image analysis. The data have been compared to the results obtained by other techniques, such as X-ray diffractometry and differential scanning calorimetry.