A method for mean crystallite size determination by X-ray diffraction line broadening was established. Both step-scanning and methods were extensivly tested and the precision of the data obtained as a function of the crystallite size is discussed. Emphasis is given to our contribution in order to eliminate instrumental effects as well as K sub(..cap alpha../sub 1/)/Ksub(..cap alpha../sub 2/) doublet effect upon line broadening. Instrumental correction was performed with a monocrystalline Si sample having mean crystallite size well above 13,000 A improving the accuracy of experimental data. Ksub(..cap alpha../sub 2/) and Ksub(..cap alpha../sub 2/) peaks determined instead of taking it for granted as 5. The mean crystallite dimension of U/sub 3/O/sub 8/ was calculated and the results show the dependence of this parameter on the quality of the microspheres.