SmFe5As3 adopts a monoclinic symmetry (space group P21/m, Pearson symbol mP18, a = 7.1848(8) Å, b = 3.8531(4) Å, c = 9.710(1)Å, β = 100.55(1)°) and is isostructural with UCr5P3. The measurement of the physical properties revealed two magnetic transitions at 30 K and 90 K. The aim of this proposal is to study the structural behaviour of SmFe₅As₃ at low temperatures with the goal of establishing a clear relationship between its structural changes and the corresponding effects on its physical properties.