Stress-strain relation is one of the most basic mechanical properties of cured rubber, and it has been studied both in academia and industry for many years. It is well known that stress-strain relation of cured rubber depends on various features of rubber compounds, such as type of polymer, type of filler, loading amount of filler, cross-link density and so on. However, there remain several problems to be fully understood for stress-strain relation of filled rubber; e.g., the effect of the structure of filler-network, filler-filler interaction and filler-polymer interaction. In this review, we explain fundamental knowledge for stress-strain relation of cured rubber both for theoretical aspect and methodology for the analysis of experimental data. Firstly, stress-strain relation of unfilled rubber (rubber without filler) is explained, then that of filled rubber (rubber with filler) is explained on the basis of fundamental knowledge for unfilled rubber. Although, various models for stress-strain relation of filled rubber have been proposed and there has not been unified understanding, we explain one of the models, which, we believe, is helpful for engineer/researcher to understand and evaluate stress-strain relations of filled rubber.