A green chemistry approach to synthesize biocompatible selenium nanoparticles is proposed in this work, using hydrogen selenite (NaHSeO3) as selenium precursor and lactose as reducing agent. The formation of nanoparticles was confirmed by dynamic light Scattering, revealing a gaussian size distribution, the maximum percentage being in the range of 20-40 nm. Zeta potential measurement indicates a negative charge -38.2 mV, the stability of selenium colloidal sol being also confirmed by UV-visible spectroscopy. TEM and AFM revealed the homogeneous, spherical shape, confirming the size of nanoparticles in the range of 20-40 nm. Structural investigations of powder selenium nanoparticles by FTIR spectroscopy and XRD patterns emphasise the presence of stretching and bending vibrations of Se-O bonds, respectively the amorphous structure of the synthesized selenium. The proposed method is suitable for biological applications such drug release, functional food or nutritional supplements.