The use of pulse laser processing to join or modify NiTi shape memory alloys has become an area of extreme interest in recent years. Until now, an in-depth investigation into the vaporization mechanisms associated with alloy composition changes during laser processing has not been done. This work systematically examines the effect of laser pulse parameters on the change in alloy composition. It was found that during conduction mode vaporization, the Ti-rich surface oxide limits the vaporization rate of Ni. This allows for less nickel loss and more control over the final composition. Additionally, keyhole formation during laser processing resulted in significantly higher rates of Ni loss, but also a greater amount of variance and reduced control of the final composition. Models are proposed that successfully predict the final bulk composition based on laser pulse parameters.