Electrical conductivity relaxation (ECR) is a very useful experimental technique for measuring oxygen transport properties of materials. It can be used to quickly and routinely assess materials performance for reactions involving oxygen ions, such as oxygen reduction reaction (ORR). ECR is commonly used to measure bulk oxygen diffusion (D) and surface exchange coefficient (k). ECReX is a Matlab based application that offers solutions to several most frequently experienced problems in practice. These include data treatment, non-ideal experimental conditions and fitting procedure. ECReX is created in Matlab 2016a and comes with an intuitive graphical user interface that will make lengthy data treatment and fitting easy, quick and user-friendly.