Abstarct: In the new century, the human resources of each organization are recognized as the most important and most valuable enterprise capital, playing a key role in achieving organizational goals and organizational success. Given the new approaches to HRM, managers have paid special attention to People Capability Maturity Model because, as we said, human resources are the most important and valuable source of an organization. One of the models in the field of human resources is human resource maturity model, which is designed to increase the People Capability Maturity. This model helps organizations identify their employees' maturity levels and prioritize them for more important tasks. The purpose of this research is to investigate the role of human resource sustainability on human resource maturity by mediating social capital and motivational capital among railway employees in north east of Iran. For this purpose, human resource sustainability questionnaires (Aibaghi et al., 2017), social capital questionnaires (Nahpit and Ghasal, 1998), the motivational capital of The researcher made and the People Capability Maturity (Mosa Khani et al., 2009) have been used for collecting data. To this end, the required data are collected from a sample of 307 North East railway employees. Validity of the questionnaires was baxsed on content validity and their reliability was calculated and validated using Cronbach's alpha method. Data analysis was performed using structural equation modeling through pls smart software. The results show that sustainability of human resources has a significant impact on People Capability Maturity, and social capital and motivational capital also have a mediating role in this relationship. Finally, suggestions were made.