In Most Developing and Developed Countries, Social Media have Covered Almost all Aspects of People's Lives. Paying Attention to Social Media Provides the Basis for Customer Orientation to Online Stores and their Loyalty. This Study Aims to Investigate the Impact of Social Media on the Loyal Behavior of Customers to Commercial Websites, Considering the Mediating Role of Customer Commitment for Online Purchases from Online Stores. This Research is Practical in Nature and Descriptive Correlational in Terms of Data Collection Method. The Statistical Population Includes Customers of Online Stores in Shiraz.To Determine the Members of the Sample, Due to the Large Size of the Community and the Fact that There Was no List of Customers, the Accessible Sampling Method was Chosen. Using This Sampling, 384 Questionnaires Were Collected With a Reliability of 0.92. And a Standard Questionnaire has been Used to Measure the Variables. The Results Showed That Social Media has a Positive and Significant Effect on the Loyal Behavior of Customers to Online Sales Websites Due to the Mediating Role of Customer Commitment. Also, the Regression Coefficient for the Relationship Between Social Media on Customer Commitment Was 0.85 and The Value of the Regression Coefficient for the Effect of Customer Commitment on Loyal Behavior was 0.83.