UP3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. U3+ is bonded to twelve equivalent P1- atoms to form a mixture of distorted face and corner-sharing UP12 cuboctahedra. There are six shorter (2.71 Å) and six longer (2.98 Å) U–P bond lengths. P1- is bonded in a 6-coordinate geometry to four equivalent U3+ and two equivalent P1- atoms. Both P–P bond lengths are 2.46 Å.