本研究探討企業集中度之變動情形及其競爭意涵，以1980至1995年間台灣製造業前一百大企業為研究對象。本研究共使用四種指標來衡量台灣製造業之集中水準，而製造業前一百大之營業淨額資料則來自於中華徵信所出版之「中華民國大型企業排名」。本文發現台灣前一百大製造業集中水準與壟斷力有逐年降低的傾向，表示台灣製造業間競爭十分激烈，而且外資企業的加入的確會使得百大企業的集中水準與壟斷力下降。以投資來源國而言，過去美資企業曾顯著增加，但近年來並無任何外資國別企業產生集中水準顯著變動的趨勢；資訊業之集中水準有明顯成長的現象，其他傳統產業則有衰退的趨勢；持續留在百大內企業，雖有「大者恆大」的現象，即企業的競爭優勢可以遞延，但此優勢並不足以成為有效的進入障礙。 This paper investigates the change of concentration ratio and discusses the implication of competition among the Top 100 firms during the period of 1980 and 1995. Using four measures of concentration, this paper finds that the level of concentration had been steadily decreasing and the competition among the leading firms in Taiwan was intensive. Though in the past, American firms had increased their representation among the leading firms, recently the entry of foreign firms did not affect the concentration ratio significantly. While the firms in the information industry increased its representation among the leading firms, the firms in the traditional industries decreased their representation in recent years. For those firms remaining in the Top 100 throughout the period, large firms tended to grow faster; and this implies that the competitive advantage of large firms could carry forward. Because the entry into and exit from the Top 100 are not unusual, the efforts to upgrade technology and engage in product differentiation by firms are going to be rewarding.