Abstract: Assays of deuterium-tritium filled glass microspheres are described.We use the natural radioactivity of tritium to determine the D-T fill.Electrons of tritium impinge on the glass shell and the substrate on which the microsphere rests.producing characteristic x rays and bremsstrahlung.These secondary x rays can be counted and then used as a measure of the tritium content in the sphere.The actual spectrum of x ray has been measured using a high-resolution Si (Li) detector with a multichannel analyzer.Si (Li) detector measurement is calibrated using the internal gas-filled proportional counter.This provides a direct measurement of total amount of tritium in the microsphere.The Si (Li) detective efficiency depends on wall thickness of glass microspheres.The system efficiency is of the order of 10-5.Once the calibration is completed,the Si (Li) detector give us a rapid,convenient and nondestructive method of determing the D-T fill of an individual microsphere.The tritium content are from 0.9 to 1.5mg/cm3.The results have been carefully compared with the method of gas bubble and both of them are in good agreement.Parameters of the microspheres.such as diameter,wall thickness,are measured with optical microscope and interferometer.Diameters are from 80 to 106μm.while wall thick ness from 0.75 to 0.80 μm.Finally,experimental results are analyzed ami discussed.