Space symmetry of prehnite, which occurs in cavities and veins within Skarn from the Tieshan iron mineral deposit, Daye, Hubei province, Central China, has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction ( CBED ) on the submicrometer scale. Our results confirm that the natural prehnite may have the structure with symmetry Pncm. The unit-cell parameters of investigated prehnite ( a = 0. 458nm, b = 0. 555nm, and c = 1. 853nm) have been calculated by using the multicrystal difiraction rings of gold, the internal standard.