Abstract Ion channeling measurements have been performed on KTaO 3:Nb (KTN) in order to check the position of Nb relative to the tantalum site. No evidence for “off-center” Nb was found in the limit of experimental accuracy. In addition, the carbon content of the samples was measured and large concentrations were found (⋍300 p.p.m. weight). Possible relationship between Nb location and carbon presence is discussed.