This research aims to analyze the effect of service quality on customer satisfaction. The subjects in this study were all people who had done blood donations in the Sleman branch of the Indonesian Red Cross for at least 3 times. This research was conducted with a total sample of 125 respondents determined by sampling techniques using non-probability sampling techniques with purposive sampling method and distributing questionnaires to respondents using Google Forms. The analytical tool used is the Statistical Package for Social Sciences (SPSS) with the SPSS 16 application program. Based on the analysis results obtained that the quality of service consisting of Physical Evidence, Reliability, Responsiveness, Assurance, and Empathy has a positive and significant effect on customer satisfaction.