Numerous EFL learners encounter diverse difficulties in speaking. Hence, this study aimed at investigating the effectiveness of an online cooperative activities (online debate and online think-pair-share) in enhancing third year preparatory school students speaking fluency. The researcher selected a one experimental group with a pre/post research design. The participants consisted of 30 male students. The current study followed the quasi-experimental design. The treatment lasted for eleven online sessions distributed on the course of three months. The experimental group benefited from the online treatment. And to investigate its effectiveness, a pre/post speaking tests were administered. In order to analyze the data, t-test was used to compare the mean scores of the experimental group's pre and post tests of fluency speaking skill(s). Moreover, the researcher utilized qualitative techniques in the current study i.e. reflection-in-action and reflection-on-action, to have the opportunity to give more comprehensive analyses to the results of the study. Results showed that cooperative online activities in EFL speaking classes had significant effects on students' overall speaking fluency and its sub-skills; mechanical skills (speed and pauses), appropriate language use skill and judgment skills (create and develop thoughts).