Online courses have been widely used to support teaching and learning in higher education. It is essential to develop methods to properly assess students in online course usages. This paper proposes a student participation index for assessing students in online courses. The index consists of a number of components, such as pages viewed and forum questions read and posted, and associated weights. It has the benefits of being non-course-specific, non-subjective, extendible and flexible. The development of the index and how it is used to evaluate students are described in the paper. Results indicate that students with higher index usually achieve better grades and vice versa.