Abstract. Laser-synthesized photoluminescent Si nanopowders, of interest for application in optoelectronics, have been studied by small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) to characterize their size-distribution function, which correlates with emission spectra and optical performances. The SANS measurements were carried out over a wide Q-range by using the D22 instrument at ILL. The analysis of the size distributions obtained from the SANS data reveals that the microstructure of such powders includes particles as large as those observed by TEM (30200 in diameter) and a distribution of tiny inhomogeneities (510 in diameter), possibly micropores, which can have relevant consequences on material performance.