The homogeneity range of the system UFe12-xSix with tetragonal ThMn12 structure was determined to extend from x = 1 to x = 3. The Curie temperature and magnetic moment depend on the silicon content with maximum values Tc = 653 K and μm = 17.5 μB per formula unit reached at x = 2.0. The thermal expansion of UFe10Si2 was investigated by X-ray diffractometry. A volume magnetostriction of ωs = 1% at T = 5 K was found. The hysteresis properties of powdered, sintered and melt-spun samples of UFe10Si2 were studied.