The purpose of this study is to develop systematic methods for evaluating the suitability of a seat and build an empirical model for predicting the suitability of a seat. The following research schemes were pursued to achieve the objectives : - Development of suitable chair dimensions - Analysis scheme for decomposing the human-product interface system - Development of model for evaluating suitability. As a result, we uncovered six dominant suitability dimensions for the design of a comfortable seat that is related to the physical dimension of a body. Here, six suitability dimensions were identified as the dimensions that represent the human sensitivity and psychological feeling on comfortable seats. Also, 43 human-interface elements (HIE`s) such as seat height, seat width, seat depth, tilting angle, seat surface etc. were investigated. HIE was generally defined as the physical characteristic of manufacturing goods, and it had close related to the body dimension of a user and environment that it was used.