We plan to determine the magnetic structure of the multiferroic orthorhombic (o-) TbMnO3 thin film deposited on (010) oriented o-YAlO3 substrate by measuring 20-30 magnetic reflections with four-circles diffractometer D10. By performing neutron diffraction experiments with the triple-axis spectrometer RITA-II at SINQ, we identified an incommensurate (IC) magnetic phase below TN ~ 41K, which locks to a commensurate phase (0 qk = 0.5 1) below Tlock ~30K. The epitaxial strain in the film changed the bulk-like IC phase (0 qk~0.29 1) to a commensurate structure. Macroscopic ferroelectric (FE) measurements on these films demonstrate large polarization (~0.4 μC cm-2) along the crystallographic a-axis below TFE ~41K. This response is in sharp contrast to the weak polarization along the c-axis in bulk o-TbMnO3 below TFE = 27 K [1]. Resolving the magnetic structure in these films will provide an intrinsic understanding of the change in microscopic mechanism induced by the epitaxial strain. The sample to be measured is a 44 nm thin (010) oriented o-TbMnO3 film.