X-ray detection is of great significance in biomedical, nondestructive, and scientific research. Lead halide perovskites have recently emerged as one of the most promising materials for direct X-ray detection. However, the lead toxicity remains a worrisome concern for further commercial application. Great efforts have been made to search for lead-free perovskites with similar optoelectronic properties. Here, we present a lead-free oxide double perovskite material Ba₂AgIO₆ for X-ray detection. The lead-free, all-inorganic nature, as well as the high density of Ba₂AgIO₆, promises excellent prospects in X-ray applications. By employing the hydrothermal method, we successfully synthesized highly crystalline Ba₂AgIO₆ powder with pure phase. Furthermore, we prepared Ba₂AgIO₆ wafers through isostatic pressure and built X-ray detectors with Au/Ba₂AgIO₆ wafer/Au photoconductive structure. The as-prepared X-ray detectors showed a sensitivity of 18.9 μC/(Gy_air·cm²) at 5 V/mm, similar to commercial α-Se detectors showcasing their advantages for X-ray detection.