Process activity mapping, a component of value stream mapping (VSM), is utilized to perform detailed process analysis to understand how to reduce and eliminate lean waste. Together with VSM, discrete event simulation is employed to confirm the effectiveness of improvements that cannot be directly observed in reducing and eliminating lean waste. This simulation study focuses on the reduction and elimination of lean waste through process activity mapping within VSM. Lean wastes were examined and developed using two simulation models: the current manufacturing system (CMS) and the revised manufacturing system (RMS), at both the macro and micro levels of VSM. The process activity mapping revealed that, out of the seven types of lean waste, four—unnecessary motion, inappropriate processing, transportation, and waiting—should be targeted to reduce and eliminate for supporting process improvement.