Words have witnessed changes in human life and trails of human thinking patterns. However, their decline also shows that human seems to be leaving history behind more quickly, judging by the speed with which some of these words fall out of use. In regard to this phenomenon, this study aims to construct a corpus to store words which have been declining or outdated in Taiwan for the past three decades, and to investigate the relationship between the decline of these words, focus shifts, and changes of lifestyle in Taiwan society.Data collected over the course of 12 months shows more than 800 political and economic related words have fallen out of use gradually or even have become obsolete in Taiwan over the past three decades. Preliminary study shows that these declined words can be classified into five categories according to their structures and meanings. In addition, the decline of these words is closely related to the development of social life. Based on data analyses, this phenomenon is believed to be caused by factors such as (1) words fall out of use when certain things and matters are no longer or rarely used or practiced; (2) words change due to changes of users’ positions and attitudes towards certain people/ matters; (3) words change due to the change of language use.