Instant messenger software including MSN、Yahoo messenger、Skype etc. have become essential as they expanded on the Internet. Instant messenger gives us convenience over traditional email. But it also has security issues, take business intranet for example: instant messenger may be a chance for information leakage and intranet virus. This thesis is intended to design and implement an instant message gateway between business intranet and MSN network. This gateway monitors and filters messages. It also functions as a web service (SOAP). The intranet instant messengers communicate with internet MSN network through this gateway using SOAP. This thesis also implements an intranet instant messenger example to make use of this gateway.