Abstract: The effects of boron addition on defect hardening at room temperature and on high temperature creep properties are investigated in the B2 NiAl intermetallic compound. It is found that boron addition is effective on increasing the room temperature hardeness on the Ni-rich side but it has no effect on the A1-rich side of stoichiometry. These observations are attributed to interstitial dissolution of boron in Ni-rich NiAl and to a lack of solubility and also due to an enrichment at grain boundaries on the A1-rich side. The similar effect is found in high temperature creep resistance of NiAl by boron addition. The high temperature creep resistance increases on the Ni-rich side but it does not affect the A1-rich side of off-stoiciometry.