The research aimed at determining the effect of work team size (number of members per team) on the effectiveness of teams working at the Scientific Agricultural Research Center (SARC) in Lattakia. This is in addition to determining the best team size for these teams. The study used the T7 Model, a questionnaire used for measuring work team effectiveness. The questionnaire was distributed on to 190 members who constituted 44 teams. The 44 teams were the study sample chosen from the whole research community which constituted the work teams in (SARC) The study revealed a number of results of which are the following: there is a significant negative correlation between team size and all the internal factors affecting effectiveness, together with significant differences between the effectiveness of small teams and big teams. However, there is no correlation between team size and the external factors affecting team effectiveness.