2005 年 6 月我國立委選制從複數選區單記不可讓渡投票制與政黨比例代表制的混合制改為單一選區相對多數與政黨比例代表的混合制，那麼，此一選舉制度的變革，究竟對立委的立法行為是否產生改變？本篇論文以立委縱貫第五、六、七屆（自 2002 年 2 月到2012 年 1 月）的提案為分析焦點，探討立委的提案行為在選制變革後是變遷或持續。本研究有幾個研究發現：首先，新選制下立委的提案更形踴躍，每個立委每會期的平均提案數大約是過去的三倍之多，且無論在哪一類型的提案數都有增多的趨勢，因此可以說新選制增強了立委原有的提案動機。其次，新選制下立委在提供普遍性利益的提案比例增加，而提供特殊性利益的提案比例降低，顯示在新選制下，由於立委必須去獲得選區 50% 以上選民的支持，因此提高了其以提供普遍性利益的立法提案，去尋求最大多數人支持的動機，此一發現支持中間選民定理，亦即在主要競爭者是兩個且在單一選區相對多數選制下，競爭者的議題立場有往中間靠攏的趨勢。然而，根據立委提案的規模與立委用在立法院的時間與資源來觀察，立委提案數的大幅提升，與提供普遍性利益的立法提案比例增加，並非意味著立委對立法問政的更加用心，也並非意味立法品質的提升。 Taiwan’s electoral system was in June 2005 reformed from a mixedsystem of a multi-member district single non-transferable vote (SNTV)plus a closed-listed proportional representation system to a mixed systemof a single member district plural system plus a closed-listed PR system.Do legislators’ representative styles and behavior change because ofthe electoral reform? In this article, I focus on the bills introduced bylegislators from the Fifth to the Seventh Legislative Yuan (from February2002 to January 2012) to explore whether legislators change or continuetheir behavior of bill introduction. Several research findings are worthhighlighting. First, legislators under the new electoral system introduceeven more bills than those under the old system. The number of billsis about three times that of before. This shows that the new system has reinforced the tendency for the legislators to have the incentive to pursue a personal vote. Second, legislators under the new system have a greater incentive to introduce general interest bills. This reflects the fact thatlegislators under the new system have a motive for attracting more than50 percent of the voters so that they are motivated to propose generalinterest bills. This finding supports the median voter theorem: under a twocompetitorrace in a single member district plural system, competitors havethe incentive to take the position of the median voter. However, most billsintroduced by legislators have only 1 to 2 articles and most of them aresmall-scale amendments so that legislators do not have to spend too muchtime and resources. Therefore, the increasing number of bills proposed bylegislators does not mean that legislators are directing more efforts towardslegislation, nor does it mean that the quality of legislation is enhanced.