Not only conventional computer system (i.e. Electric Medical Record, Physician Order entry, PACS), but also other medical equipment including ECG,US, EEG, X-ray and many others, are on-line now. Extensive use of computer network exacerbates complexity of programming computer network equipment. While healthcare service becomes more dependent on information technology, such complexity can result in network failure that interrupts health service. Recently, concept of Software Defined Network (SDN) has widely been accepted by network equipment supplier and production quality network equipment appeared in the market. SDN is a concept of programmable computer network fabric, in other words, network that can be dynamically reconfigured by downloading the settings from the controlling computer. We have introduced SDN in our hospital network to evaluate its utility and stability. After introduction of SDN, SDN segment turned out to be stable, and automatic rerouting avoiding failed route was far quicker than conventional technology. Our conclusion is SDN is highly valuable technology in healthcare, that is 24hr/365day mission critical business.