Sr(1-x)Bi(2+y)Ta(2)O(9) (x, y=0.2, 0) nanoparticles, synthesized by a sol-gel method, are investigated by X-ray diffraction and Raman spectroscopy. Large structure distortion shows the size effects in nanoparticles, which gives rise to the Raman bands broadening. The Bi content is the most important factor responsible for non-stoichiometric SrBi(2)Ta(2)O(9) structure distortion and providing the larger ferroelectric spontaneous polarization and the higher Curie temperature. The stability of the crystal structure is discussed in consideration of inner compressive stress in nanoparticles.