Bi3+ substituted garnet nanoparticles Y3-xBixFe5O12 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.3) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), IR spectroscopy, thermal gravity analysis-differential thermal analysis (TG-DTA), transmission electron microscope (TEM), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The XRD patterns Of Y3-xBixFe5O12 have only peaks of the garnet structure. From the results of VSM, it is shown that the saturation magnetization of sample is decreased with increasing the content of Bi ions. Meanwhile, it is observed that with the enhancement of the single magnetic domains surface spin effects, the saturation magnetization is raised as the particle size of samples is increased. (c) 2007 Elsevier B.V. All rights reserved.