The crystal structure of sodium biselenite has a monoclinic unit cell with a =2 1.84 A, b = 5. 80 A, c = 10.30 A, β = 101°30', which contains 16{NaHSeO3}. The spacegroup is C2h6 - I2/a .The parameters of Se atoms have been derived from Patterson projections P(uw) and P(vw). With these parameters, Fourier method has been applied to locate Na atoms and O atoms. The Fourier projections ρ(x , z) and ρ(y , z) comfirm the structure. (Fig. 2. and Fig. 3.)The present work reveals that, the crystal of sodium biselen...