This　paper　considers　a　cooperative　output　regulation　design　for　a　class　of　multi-agent　nonlinear　systems.　For　this　problem　under　undirected　communication　topologies,　the　previous　studies　have　shown　that　some　internal　model　principle　based　smooth　distributed　control　law　can　be　constructed.　In　this　study,　we　show　an　attempt　of　an　event-based　protocol　by　a　cooperative　practical　output　regulation　approach.　©　2017　Technical　Committee　on　Control　Theory,　CAA.