A study was performed on the effects of oxygen content in shielding gases on weld microstructures and properties during laser welding of commercially pure (CP) titanium thin sheets. The experimental results, mainly analyzed by optical and scanning electron microscopy and mechanical testing, have indicated correlations between weld surface color, microstructure and mechanical properties (strength, ductility, hardness, etc.). As the oxygen content increased, the weld surface color changed from silver, straw to blue while the surface hardness increased. On the other hand, with the increasing of oxygen content, the tensile strength increased first and then decreased because of the brittle microstructure introduced. Practical guidelines were also provided, based on the study, to deal with shielding deficiencies in laser welding of medical components of CP titanium sheets.