In most of WebGIS applications, user interactions mainly concentrate on map data editing or data querying. Another aspect with paying less attention is to allow user doing spatial analysis. Spatial analysis can be implemented on server side, by using WPS (Web Processing Service), or on client side, by using JSTS (JavaScript Topology Suite). As an contribution to this aspect, this paper shows how to use to use WPS service of Geoserver and JSTS JavaScript library to carry on spatial analysis activities. A WebGIS system - based on the open source Geoserver and OpenLayers - has been developed and used to perform spatial analysis, searching for spatial features that have spatial relationships with other spatial features. Experiment result shows that the use of WPS and JSTS to perform spatial processing over the internet is practically doable.