The quality of service may determine the sustainability of an organization, and this includes the quality of lecturer services both in private and state universities. This research aims to model a quality service instrument which respectively consists of literature reviews, interviews, expert opinions, and a test instrument application based on Rasch modeling. The respondents of the study were students at Pakuan University, West Java, whereas 534 samples were taken. The result of this study reveals that there are 5 dimensions of service quality along with 27 items. Several items due to the students’ demographics and the impacts on service quality improvement at private universities are not fully confirmed by students