As WWW becomes the representative service of Internet, HTML has revealed it's limitation on processing multimedia data. Many other techniques - like DHTML and Java - were introduced. They, however causes heavy traffics on the network and overhead on web browsers. The Synchronized Multimedia Integration Language (SMIL) is a recommendation from the W3C that makes authoring of TV-like multimedia presentations on the Web easier. It is derived from the eXtensible Markup Language (XML) to define a set of markup tags to synchronize the timing and positioning relationships between multimedia objects. This paper presents the design and implementation of a SMIL-based web editor. The proposed editor handles well the temporal and spatial synchronized information among multimedia objects. It was, especially designed for multimedia teaching aids. The easy user interface and convenient tools are the essential needs for the teachers unfamiliar to the multimedia authoring. Then the user interface with WYSIWYG and Drag & Drop is the main theme in designing the SMIL editor. Now novice users are able to make complicated multimedia presentation in more ease and convenience.