In this proposal, we propose to investigate the spin dynamics in the complex material BaFe2Se3. This material presents low dimensional magnetisme below 250K, combined with unusual orbital selective Mott insulator properties. Such a unique combination results in a difficult problematic on the magnetic properties of this system. Indeed, the spin dynamic on this system may require a theory beyond simple spin-wave theory. By measuring magnetic excitation on a single crystal of BaFe2Se3, we propose to obtain an exhaustive picture of magnetic excitations that will be compared to different models.