The plastic deformation mechanisms of the titanium single-crystal nanopillars under both tension and compression were studied with the molecular dynamics simulation method. In this work, the research focuses on two aspects around the microscopic deformation mechanisms: stress-strain analysis and the evolution of atomistic configuration. The results indicate that the {101 ?2} twinning and stacking fault dominate the tension deformation along the [0001] direction. The slip is the principal factor leading to the initial yielding and then the pyramidal slip occurs to coordinate both vertical and horizontal strains for the compression condition along the [0001] direction. Additionally, no twinning is found in compression. Besides the conventional {101 ?2} plane, semi-coherent basal-prismatic interfaces between parent and reoriented crystal were also observed under tensile loading.