A Laves phase Ir2Y is found to exhibit a temperature dependent solubility, which yields Ir3Y precipitation within the Ir2Y matrix of an arc-melted Ir-30at.%Y alloy. Microstructure observations have confirmed that the precipitation of Ir3Y has already started in the as-cast state. Upon annealing of an as-cast Ir-30at.%Y, the volume fraction of Ir3Y precipitates increases and finally reaches about 50%. The orientation relationship between Ir3Y and Ir2Y has been identified as: (0001)Ir3Y//(111)Ir2Y and [21 _ 1 _ 0]Ir3Y//[1 _ 10]Ir2Y. The orientation relationship is rationalized by the atom matching at the habit plane between the two phases.