This paper presents a review of current research, both theoretical predictions and experimental measurements, on the mechanical properties of carbon nanotubes (CNTs). The emphasis has been given to the tensile strength and Young’s modulus. Deformabilities including buckling, bending, and twisting are also examined. The predicted and measured values of mechanical behaviors of CNTs are compared and an analysis on the variation of the values is made. The challenges facing the research of mechanical properties of CNTs are stated. CNT reinforced composites are involved as well in the paper. A thorough understanding of the properties of CNTs helps exploring full applications of this unique group of materials.