Opimon is a visualization tool which can monitor and visualize an OpenFlow network. Opimon provides the topology graph of the OpenFlow network and also shows flow table information of each OpenFlow switch. This software is used for visualizing PRAGMA-ENT environment. Opimon is developed by Wassapon Putchong’s student in Kasetsart University (Thailand). He demonstrated the visualization tool at PRAGMA 31 meeting in Bangkok. The tool is really helpful to operate an international SDN-testbed like ENT.