The service of mobile communications is customer-oriented. The service is intangible and filled with large amounts of variable. It causes the difficulty of evaluation on service quality. Therefore, understanding customer requirements and key factors of service to promote service quality, meet customer needs, retain customer loyalty and create profits is one of the important issues in mobile communications. The study mainly aimed to discuss the service quality of mobile telecommunications industry. According to the revised SERVQUAL measure table proposed by Parasuraman et al. (1991), the service quality questionnaire is designed by service characteristics of mobile telecommunications industry.The total number of the questionnaires was 162. Questionnaires were finished via web survey, discussing the influences on demographic variables and whether there were significant differences between customers¡¦ expectations and their authentic experiences. The Importance-Satisfaction model (I-s Model) and Improvement index (Ii) were also used as references to find out the priority to improve. Based on the survey consequence, there were significant differences between customers¡¦ expectations and their authentic experiences. There were 22 questions (23 questions of 5 dimensions) showing significant differences except for the good brand image of the enterprises. Therefore, the assumption that customers¡¦ expectations and their authentic experiences was significantly different in terms of service quality was partly tenable. When it comes to the expectations of quality, the results showed significant differences in tangibles (gender), responsiveness and assurance (monthly income); besides, there were also significant differences in responsiveness (age) and empathy (residence) when it comes to quality awareness. Consequently, the assumption is partly tenable. Moreover, customers¡¦ expectations are always higher than what enterprises can actually provide, which means these enterprises cannot satisfied with what customers¡¦ needs due to internal resources and social environment of the enterprises of mobile telecommunications industry. In order to improve these issues, Importance-Satisfaction model (I-S Model) and Improvement index (Ii) were used to make an improvement project listed in priority. The result shows the mobile network quality is the most important and also the most dissatisfied item for the customers. It could be provided to mobile communications as a reference to improve for promoting customer satisfaction and loyalty.