Polarisation microscopy and dynamic light scattering were used to study the dynamical behaviour of disclination lines in a thin nematic film of 5CB. Our experiments show that the lines exhibit thermally excited diffusive motion with the ends of disclination lines being pinned to the surface. In the dynamic light scattering experiments a process with a broad distribution of relaxation times was' observed, which was due to the diffusion of the disclination lilies with different lengths and orientations. Palarisation microscopy was used to follow the time dependence of the displacement of a single disclination line, which enabled the measurements of the diffusion coefficient and the line tension of the disclination lilies in the samples.