As computer-related technologies have been developed, legacy design systems have not been appropriate far new computing environment. It is necessary that most of them are either modified or newly developed. However, these activities require quite much amount of cost and time. This paper presents a method of extending legacy design systems to the internet without any modification using XML and XSLT. We have been extended legacy systems in the two viewpoints. First, an XML document has been defined to present the input information of a legacy system which is executed on the consol environment - MS DOS, for example. Also, an XSLT document has been generated to transform an XML document to the input document of the legacy system An XML document is transformed to the input document by XSLT processor according to the transformation rules defined in the XSLT document. This technique to generate input documents is independent to the platform type and facilitates to link legacy systems to other systems. Second, a legacy system controller has been made to control a legacy system and developed a web service to extend it and its controller. The legacy system controller operates it automatically. The web service provides its functions to other systems via internet. We have applied the developed methodologies to the legacy gear design system 조ich calculates AGMA gear rating md made AGMA gem rating web service.