In order to apply continuum damage mechanics to model the damage, fatigue, and life of rail steel used for the JIS 50kg N rail, some parameters had to be developed based on its stress-strain curve and S-N curve. Using these parameters, numerical analyses successfully reproduced these curves, which would allow the life span values to be obtained through analysis. Results from the analysis compared favorably with those from experiments, demonstrating that an analysis based on damage mechanics can be a successful predictor of rail fatigue and rail life. An outline of damage mechanics is given within the limitations of the formulation used in this analysis, and the procedure for determining the parameters and the results of the determination are presented. The stress-strain curve and the S-N curve of rail steel are experimentally obtained by using test pieces of 50 kg N rail. Finally, a three-point bending test of a square bar prepared from a rail was conducted and the experimental life was compared with what the damage mechanics analysis predicted. Conclusions and issues for further investigation are also presented.