We have measured the Young's modulus of long aligned carbon nanotube ribbons using a special stress-strain puller designed for whisker-like materials. The Young's modulus of the graphitized carbon nanotube ribbons is about 60 GPa, which is 2.5 times higher than that of the as-grown ribbons. This suggests that the graphitization is an effective way to improve the mechanical properties of the ribbons. Most of the measured ribbons are semiconductor and their resistivities are in the range of 4.4-12.6 x 10(-4) Omega cm. An interesting phenomenon appeared in one ribbon is that the electrical property of the ribbon changes from metallic to non-metallic with decreasing the temperature. (C) 2002 Elsevier Science B.V. All rights reserved.