The magnetoresistance of textured and non-textured polycrystalline thin films of La 0.7Sr 0.3MnO 3 has been measured in pulsed magnetic fields up to 60 T between 4.2 and 300 K. The non-textured film shows a linear increase with increasing field of the magnetoconductance at low temperatures which is attributed to a constant high-field susceptibility at grain boundaries (GB). The time dependence of resistance has been recorded starting ∼10 ms after the field pulses. For both polycrystalline films, logarithmic relaxation and an unexpected increase of the relaxation rate with decreasing temperature down to 1.9 K is observed. This type of relaxation is absent in an epitaxial film of La 0.7Sr 0.3MnO 3 and smaller for the textured one of the polycrystalline films, indicating its origin in a structurally disturbed layer between misaligned grains. It might be caused by a spin glass-like state at some of the GB within the conduction path.