Over 1.0 mm boron nitride nanotubes (BNNTs) were successfully synthesized by an optimized ball milling and annealing method. The annealing temperature of 1100 degrees C is crucial for the growth of the long BNNTs because at this temperature there is a fast nitrogen dissolution rate in Fe and the B/N ratio in Fe is 1. Such long BNNTs enable a reliable single tube configuration for electrical property characterization and consequently the average resistivity of the long BNNTs is determined to be 7.1 +/- 0.9 x 10(4) X cm. Therefore, these BNNTs are promising insulators for three dimensional microelectromechanical system. (c) 2008 Elsevier B.V. All rights reserved.