Although　teamwork　shows　stronger　innovation　ability　than　individuals　and　this　advantage　has　been　increasing　over　time,　the　negative　effects　of　larger　teams　also　appear　as　the　number　of　inventor　members　increases.　This　study　discusses　the　double-edged　sword　role　of　inventor　teams　in　innovation　quality　at　two　extremes:　the　high　quality　and　the　low　quality.　We　argue　that,　inventor　team　size　influences　innovation　quality　because　diversity　works　in　the　evolutionary　process　of　innovation,　but　different　types　of　diversity　play　distinct　moderating　roles　in　these　relationships.　Using　patent　data　from　the　US　pharmaceutical　industry,　empirical　results　show　that　there　is　an　inverted　U-shape　relationship　between　inventor　team　size　and　high-quality　innovation,　and　a　negative　relationship　between　inventor　team　size　and　low-quality　innovation.　These　relationships　are　moderated　at　different　degree　by　technological　and　geographic　diversity.　Our　findings　contribute　to　existing　literature　of　innovation　and　also　provide　meaningful　implications　for　innovation　management.