One of the main tasks in mechanical design is to prevent it from experiencing resonance. For this task, we need to know the natural frequencies of the components or mechanical systems. This chapter will show how to use the “Frequency” module in SolidWorks Simulation to estimate the first five natural frequencies. Natural frequency is dependent on the material, dimension, and type of fixture, and is independent of loading. When there are some rigid motions for the component under the simulation, the number of frequencies we need to solve will be the number of rigid motions plus 5, so that the first five natural frequencies can be obtained. For frequency analysis on an assembly, there are only two types of contacts in SolidWorks Simulation. They are “Bonded” and “Free”. For the bonded interactions, the components on any connected interface will be treated as if they are welded together. For the free interactions, the analysis separates the assembly on the connected interfaces into different sub-systems or several individual components for frequency analysis. Several examples with step-by-step instructions are presented to demonstrate how to run natural frequency analysis.