Quantum measurement remains puzzling through the mist of its stormy history from the early birth of quantum mechanics to state-of-the-art quantum technologies. There were two competitive measurement schemes that have been widely tested in a variety of quantum phenomena: von Neumann’s projective (‘strong’) measurement (1936) and Aharonov’s weak measurement (1988). Here, we report the observation of measurement transition from weak to strong in a single trapped 40Ca+ ion system. By realizing a macroscopic superposition state of the ion's vibrational motion by pre- and post-selecting its internal electronic state, we observed the transition from weak value to expectation value asymptotics. More precisely, the weak-to-strong measurement transition is characterized by a universal transition factor, where is a dimensionless coupling parameter related to the system-apparatus coupling. This transition, which continuously connects weak measurement and projective measurement, is capable of opening new experimental possibilities for testing quantum foundations, as well as novel applications for weak-valued state tomography and simulation in trapped ions and other physical systems.