Internet GIS sites are currently being emersed as one of important places to acquire spatial information in stead of traditional paper map. This paper is intended to identify critical factors in evaluating internet GIS site quality. While there should be a considerable number and variety of factors associated with internet GIS site quality, this paper focuses on the site characteristics that generate visitor satisfaction. After carefully reviewing the previous literature of general website evaluation, four criteria that are critical to internet GIS site quality were identified: (1) contents (2) design (3) navigation (4) spatial analysis. An empirical study for a case study site has been conducted to confirm the validity for the four evaluation factors. A site diagnosis by the criteria provided many valuable information for Web site quality. For example, it was found that many symbols in the site made the visitors confusing and navigation interface was not very user-friendly to track required positional information due to inconsistency in terms of cartographic concept. The results indicate that the evaluation criteria may be used not only as a tool to evaluate internet GIS sites, but also as a checklist to improve the quality of a web site that is under development and requires remodelling. As a result, the research findings have established the new concept of ‘the quality assurance of the internet GIS site’, proposed as an initial aim of this paper Many of the issues unresolved in this project could be improved, based on the understanding of the four criteria suggested in this paper.