Silicon-iron alloys with silicon content about 6.5wt.%Si offer a great potential for applications aiming reduction of core loss in electric parts. Deposits of the Fe-6.5wt%Si alloy produced by spray forming were annealed at temperatures between 400 and 1300oC, during 1h in vacuum. The grain size has a great importance to the magnetic properties. In the present work, it was analyzed the influence of the metallography parameters in order to get the best accuracy to determine the grain size according to ASTM 112-96. Chemical composition, time and temperature of specific etchings were modified and tested in different conditions of observation in light microscopy. Bright field, polarized light and dark field were used in the samples aiming to measure the grain size. The best etchings were Nital 10% and Marshall, both at room temperature. The results of grain measurement are presented in their relationship with the magnetic properties.