The aim of the study is to explain the students’ off-task and on-task participation during an extending English learning through WhatsApp. So, the researcher did a study which used qualitative single case study approach to five undergraduate students of Islamic University in Semarang who have emotional relationship. The study used content analysis to categorize the postings based on the task type: off-task and on-task by numbering them with different colours. The study resulted that students' social interactions (off-task) were fluctuant and the on-task participations increased over three sessions. Though the intensity of the off-task participation didn’t determine the on-task participation, but all the participants actively took part in both off-task and on-task participation.