Abstract: The uranium-radium (U-Ra) equilibrium coefficient is a significant correction parameter for the resource and reserve estimation of in situ leached (ISL) sandstone uranium deposits, directly influencing the accuracy and scientificity of such estimations. Employing a high-purity germanium gamma-ray spectrometer, this study determined the U and Ra contents of 1 431 samples from the Manglai uranium deposit in the Erlian Basin, yielding U-Ra equilibrium coefficients for these samples. Statistical analyses were performed on the U-Ra equilibrium coefficients in terms of frequency distribution, U content, grain size, lithology, and spatial distribution, to explore the primary factors influencing the changes in U-Ra equilibrium coefficients and their implications. The results indicate that the Manglai uranium deposit showed a U-Ra equilibrium coefficient of 0.85, suggesting that the deposit is significantly richer in U. The U-Ra equilibrium coefficient was negatively correlated with U's concent and grade. Additionally, the U-Ra equilibrium coefficient exhibited distinct vertical zoning within ore bodies. Within uranium-mineralized sand bodies, the most favorable grain sizes were observed in sandy conglomerates, coarse- and fine-grained sandstones. The presence of grayish-black and dark black mudstones contributed to uranium enrichment and mineralization in adjacent mineralized sand bodies. The block I-1 in the southern main ore body exhibits significant uranium enrichment potential and the highest U enrichment degree. The uranium deposit is overall richer in U, with almost no Ra-richer zones, indicating that the uranium deposit experienced minimal oxidative transformation after its formation. The results of this study provide a scientific basis for the subsequent construction arrangement of in situ leaching at the Manglai uranium deposit while contributing to a deeper understanding of the deposit's mineralization regularity.