A novel synthesis of uranium tetraboride (UB4) by solid-state metathesis reaction is demonstrated. This approach significantly lowers the temperature required to synthesize this material to less than or equal to850 degreesC. When UCl4 is reacted with 2 equiv of MgB2 at 850 degreesC, crystalline UB4 is formed. Powder X-ray diffraction and ICP-AES data support the reduction Of UCl4 to UCl3 as the initial step in the reaction. The UB4 product is purified by washing with water.