Maintaining customers, there must be a need to make your customer satisfied with your company. Maintaining customers are hard, because changes in taste always occur. What customer need, what customer wants, it is all depending on what is currently happening in the environment. If there is no customers, there will be no business organization. In order to increase the number of customer, developing customer satisfaction and customer loyalty is very important. This study aims to measure the effect of customer satisfaction towards customer loyalty at PT Sinar Abadi Motorindo Medan. This Final Paper can also be applied to company that in the same field. The research method that is going to be applied by the writer is quantitative analysis method. The data used through this research are primary data and secondary data. Data collection is using questionnaires and interviews. The questionnaire was distributed to 67 customer of PT Sinar Abadi Motorindo in Medan for a month. This research uses convenience sampling method by collecting data only when the writer is able to collect the data. Likert Scale has been used to measure variables. The simple linear regression equation of Y = 9.892 + 0.397 x, shows customer loyalty increase positively when there is an increase in customer satisfaction. According to the research by writer on determination test R square which shows 0.591. This shows customer satisfaction has 59.1% effect on customer loyalty. The rest 40.9% can be affected by other variable that is not included in this final paper