Mo3Si single crystals were successfully produced using an optical floating zone furnace. Reoriented specimens were-obtained from the original crystal with < 111 >, < 110 > and < 100 > orientations. Cracking behavior of the crystals shows an interesting relation regarding their crystal orientation. Fracture toughness values show small orientation dependence. The hardness test shows that the hard plane. is the (10-0), and the softest plane was the (110) and not the (111) as it was expected. (C) 2008 Elsevier B.V. All rights reserved.