Sultan Iskandar Muda Airport (SIM) is located in Aceh Besar District, Aceh Province. It is crucial to analyze Airport service quality analyzed to evaluate the level of passenger satisfaction. This study aimed to evaluate the level of passenger satisfaction using the Customer Satisfaction Index (CSI) and gap analysis. Data collection was conducted by administering online questionnaires to respondents who have used airport facilities. The measurement employed the Likert scale. The results showed that the most dominant characteristics of respondents were 18-27 years old (64%), male (52%), and the latest educational level of senior high school or equivalent (46.5%) and students (60.6%). The results showed that The CSI scores was less than 100% and the gap value was negative based on the 23 indicators of service performance. This finding indicates that Sultan Iskandar Muda Airport has not provided satisfactory service to passengers. The lowest assessment were on the indicator of information and availability of health service facilities (I2), information of flight disruption and compensation (I14), facilities for disabilities (I22) and nursery rooms (I23). Thus, the capacity and quality of all indicators, especially the lowest 4 indicators, need to be improved.