This paper presents a simulation model for assessing the mutual impacts of Engineering Change Management (ECM) process and New Product Development (NPD) process on each other. The discrete-event simulation model incorporates ECM into an NPD environment by allowing Engineering Changes (EC) to compete for limited resources with regular NPD activities. The goal is to examine how the relative size and frequency of NPD as well as ECM, NPD process structure (in terms of overlapping and departmental interaction), and the operational policy of resource using priority that one organization employs affect lead time and productivity of both NPD and ECM. Decision-making suggestions considering EC impacts are drawn from an overall enterprise system-level perspective based on the simulation results.