The phase transition of U2Zn17 at 9.7 K has been investigated by neutron powder diffraction. The transition corresponds to the onset of antiferromagnetic order where the U moments are oriented antiparallel to their nearest neighbors within the basal planes and the near neighbor along the c^ axis of this rhombohedral compound. At 5 K, the ordered moments lie within the basal planes and are of magnitude (0.8±0.1)1/4B, which is substantially below the paramagnetic moment of 2.251/4B/U atom given by high-temperature susceptibility data. © 1986 The American Physical Society.