Irradiation effect by slow neutrons at a low fluence of about 108n/cm2 on YBCO and GB-CO films was reported in this paper. It was experimentally shown that appropriate slow meutron irradiation would increase the critical current densities Jcm at higher temperature (78K) and have almost no effect on Jcm at lower temperature (57K). Peak effect deduced by appropriate irradiation was observed in the field dependence of Jcm and volume flux pinning force density Fp at 78K. Based on mechanisms of slow-neutron irradiation , some discussions were made. Irradiation effect by slow neutrons at a low fluence of about 108 n / cm2 on YBCO and GB-CO films was reported in this paper. It was experimentally shown as appropriate slow meutron irradiation would increase the critical current densities Jcm at higher temperatures (78K) and have almost no effect on Jcm at lower temperature (57K). Peak effect deduced by appropriate irradiation was observed in the field dependence of Jcm and volume flux pinning force density Fp at 78K. Based on mechanisms of slow-neutron irradiation, some discussions were made .