In the twenty-first century, online learning has evolved as a worldwide platform to connect, collaborate and engage users in the learning process. Online learning today is integrated with social network connectivity, which builds an ecosystem for interaction between students, teachers, and professors from every corner of the world, providing them with free and accessible online resources. However, in order to promote active engagement of the learners and delivery of meaningful learning in the online learning settings, it is also necessary to determine students' perceptions towards online learning. The aim of this study was to develop a scale for determining students' perceptions of online learning (POSTOL). This scale consists of four dimensions: instructor characteristics, social presence, instructional design, and trust. Research data was collected from 208 Taiwan university students. In order to determine the validity of the scale, exploratory factor analysis, and confirmatory factor analysis and item discrimination was used. Results showed that the POSTOL is a valid and reliable instrument. The implications of the present study are important for instructional designers, educators, and institutions that are planning to offer, or are currently offering, online courses.