Amongst the non-aluminium based quasicrystalline alloys, investigations of titauimn containing alloys in regard to tim o(:currence and stability of quasicrystalline phases haw~ aroused con~siderable interest in recent years. Employing X-ray and TEM techniques a systematic investigation of the iIfi-luence of substitution for Fe by Si and Ni on tile stability of icosahedral phase ill rapidly quenched Fe-Ti alloy has been carried out. The occurrence of metastable phases including c~)mmensurately modulated phase and the deeagonal ph~e in Fe-Ti-Si system have been found. In addition, the occurren(:e ofstructural disorder mauifested by arcs of diffuse scattering in diffraction patterns and anisotropy in the shape of idffracti(~n spots has also been pointed Β’)ut. It has been observed that 6 at.% of Si in Fe-Ti-Si system results in the formation of single-ph~-~e icosahedral quasicrystals. We have shown that contrary t() some earlier reported results on Ti2Ni, Ti2Ni(Si) and Ti.~GNi23Fe.~Sil~ alloys do not p()ssess the i(:osahedraL phase. In Ti~Fe26_=Ni,Si6 alloy system, icosahedral phase formation ability is limited to the value of x< 9. The occurrence of icosahedra] pha.se in these alloy systems h~s been analysed in teIIns ()f e/a rati().