Abstract Rolling contact fatigue in bearings, gears, and railway tracks is a common problem experienced in many industrial applications. Given the stochastic nature of fatigue failures, design predictions are generally complex and difficult. Thus, engineers rely on extensive testing to establish design baselines and empirical analysis-equations. The objective of the work presented here is to provide detailed information in the design and validation of a variable slip ratio rolling contact fatigue (VSR-RCF) tester. The tester has three major components: (1) a mechanical system, (2) a control system, and (3) a data acquisition system. All the components are designed and intergraded to provide a fairly reasonable testing time and dry to submerged lubrication testing conditions. The major characteristics of the VSR-RCF tester are the variable slip ratio and the ability to accommodate different sizes and types of specimens. A mandrel and live center are used to hold the specimen while two hydraulic rollers apply the load. Failure is detected with an eddy currents crack-detection system. Preliminary tests on a common gear material (AISI 8620 steel) were performed to assess the mechanical limits as well as the control system software performance. Detailed development and validation of the tester are discussed along with servo drives and electronic gear ratios (EGR).