Bead on plate Friction Stir Welding (FSW) was applied in the current study in order to simulate butt welding of CP Ti. Ti, due to its high melting point requires a WC welding tool and high welding parameters. After obtaining the optimal welding parameters, X-ray inspection showed that the FSW’ed material was free of defects as well as from WC particles that may have originated from the welding tool. Comprehensive optical and Scanning Electron Microscopy (SEM) metallographic characterization together with micro hardness tests were performed on each of the different zones of the welded joint, namely, the parent material, the Heat Affected Zone (HAZ), the Thermo-Mechanically Affected Zone (TMAZ), and the stir zone. Tension tests and fractography studies were carried out on both parent material and FSW'ed material. Grain refinement and mechanical twining were detected within the TMAZ and the stir zone, these microstructural changes considered to be responsible for the improved mechanical properties of these zones. Transmission Electron Microscopy (TEM) conducted in order to investigate the microstructural changes during welding revealed the existence of nano-sized grains in the FSW’ed material due to dynamic recrystallization (DRX) occurring during welding. The current study contradicts previous correlations, proposed by several researchers, between the conditions prevailing at different points across the weld seam and the microstructural changes occurring. The occurance of microstructural changes during welding as well as their influence on the mechanical properties will be referred and discussed.