The results of magnetoresistance (MR) and resistance relaxation of nanostructured La_1-xCa_xMnO₃ films, with different composition x grown by metal-organic chemical vapor deposition technique, are presented and compared with the La_0.83Sr_0.17MnO₃ films. The MR was investigated in pulsed magnetic fields up to 60 T in the temperature range 1.5-294 K while the relaxation processes were studied in pulsed fields up to 10 T and temperatures in the range of 80-300 K. It was demonstrated that at low temperatures the MR has higher values in the LCMO films in comparison with the LSMO ones, while at room temperatures, the highest MR values are obtained for the LSMO films. The fast (∼100 μs) and slow (∼ms) resistance relaxation processes were observed after the magnetic field pulse was switched off. It was shown that the fast process could be analyzed using the Kolmogorov-Avrami-Fatuzzo model, considering the reorientation of magnetic domains into their equilibrium state, while the slow process - by the Kohlrausch-Williams-Watts model considering the interaction of the magnetic moments in disordered grain boundaries having spin-glass properties. It was concluded that La_1-xCa_xMnO₃ films having a higher sensitivity and lower memory effects and should be favored for the development of fast pulsed magnetic field sensors operating at low temperatures.