The splitting of band structure and absorption spectra, for silicon nanotubes (SiNTs) under axial magnetic field, are studied using the tight binding approximation. It is found that band splitting is approximately proportional to the magnitude of magnetic field as _E Eg = νii _0 where νii is the splitting rate. For Si g-NTs, we calculated the splitting rate of the two first bands nearest to the Fermi level in the _ point and found that it can be fitted with a two degree polynomial as νii = _2 =0 ai j xj where x = 1 n2 and for sufficiently large diameter Si g-NTs, the νii can be fitted by a linear function. For semiconductor Si h-NTs the ν11 = 6 but ν22 and ν33 show radial dependence. Also we found that magnetic field leads to splitting for all peaks in the low energy ranges for all zigzag Si h-NTs and Si g-NTs. The first peak of group (I) of Si g-NTs does not show any splitting in the magnetic field and for all metallic Si h-NTs, the less than 0.2 eV where this peak arises from energy gap created around Fermi energy.
