The phases, lattice parameters and linear coefficient of thermal expansion were determined by X-ray powder diffraction between room temperature and 873 K for the system HoNi5 −xAlx (3 ≥x≥ 0). Alloys were hexagonal, in the space group P6/mmm; for 2 ≥x≥ 0 they were isostructural with CaCu5, and for 3 ≥x≥ 2 they were isostructural with YCo3Ga2. In both cases, the unit-cell parameters a and c increased as the Al content increased. The linear thermal expansion coefficient was composition dependent. Each of the investigated alloys exhibited an anisotropy in thermal expansion, the linear expansion coefficient along the a axis being larger than along the c axis.