Abstract: Objective This study aims to investigate the early-stage impact of acute localized cobalt-60 irradiation on functional connectivity in rat brains using functional magnetic resonance imaging (fMRI). Methods An 11.7 Tesla small-animal MRI system was employed to evaluate regional brain activity in radiation-exposed rats through blood oxygen level-dependent (BOLD) fMRI. Initially,changes in the topological properties of the brain network following irradiation were analyzed using a small-world network model. Subsequently, Pearson's correlation analysis was conducted to quantify the functional connectivity(FC) strength between specific brain regions, thereby assessing alterations in inter-regional information transmission and identifying key affected brain regions. Furthermore, Kendall's coefficient of concordance(KCC) was calculated to measure regional homogeneity (ReHo) within these key brain regions. Finally,the fractional amplitude of low-frequency fluctuations (fALFF) was computed for the key brain regions. Results Ours results demonstrated that, when compared to the Sham group, no significant differences were found in global or nodal topological properties of the rat brain functional network 2 d after 30 Gy acute localized ionizing radiation. However, a statistically significant increase in FC strength was observed between the left retrosplenial cortex and the right septal region. No significant changes in ReHo values were detected in these key regions. Additionally, the fALFF value in the left retrosplenial cortex was significantly elevated, while no significant change was observed in the right septal. Conclusions In conclusion, acute localized ionizing radiation at a dose of 30 Gy significantly enhances long-range functional connectivity between the left retrosplenial cortex and the right septal region, along with increased neuronal activity in the left retrosplenial cortex. These effects may be attributed to the compensatory responses caused by acute ionizing radiation.