Superconductor samples of type (CoFe 2 O 4 ) x GdBa 2 Cu 3 O 7δ (0≤x≤0.1) were synthesized by the conventional solid-state reaction technique, whereas nanosized CoFe 2 O 4 was prepared by co-precipitation method with grain size of about 8.5 nm. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE). The temperature dependence of real ( ) and imaginary ( ) components of AC magnetic susceptibility (ACMS) at different magnetic field amplitude (3-15 Oe) was investigated. The analysis of the temperature dependence of ACMS was performed using Bean critical state model. The values of the critical current density c J at T > p T ( p T is the inter-granular loss peak temperature) were calculated as a function of magnetic field and nanosized CoFe 2 O 4 content. It was found that the low nanosized CoFe 2 O 4 addition content (x = 0.01) improves the critical current density c J of Gd-123 superconducting phase. The observed variation of c J with temperature indicated that the weak links are changed from superconductornormal metal-superconductor (SNS) for free sample to superconductor-insulator-superconductor (SIS) type of junctions for samples added with nanosized CoFe 2 O 4 of x > 0.01. We also discussed the experimental results in the framework of the critical state model to estimate the effective volume fraction of the grains g f using Cole-Cole plots.