歷經第二次伊拉克戰爭與經濟危機，冷戰後主導世界秩序的支配強權－美國國力遭受打擊，進而出現美國衰落的論述；同一時期，太平洋另一端新興大國—中國藉由快速的經濟發展在世界舞台展露頭角。因應此國際情勢而生的「權力轉移理論」便是探討既存支配強權與新興崛起挑戰者間權力轉移過程的理論。權力轉移論者認為，當新興挑戰國的能力增強至足以與既存支配強權匹配時，若同時其對現狀滿意度越來越低，便可能觸發戰爭。然而，國際政治受各區域國家所牽動，兩強間分庭抗禮且須考量區域中舉足輕重的領導國家。傳統上拉丁美洲被視為美國後院，而中國對該區域各國互動密切，更有論者提出中國直搗美國後院一說。綜觀拉美各國，其中擁有豐富天然資源、作為美洲第二大經濟體的巴西，是首屈一指的區域領導國家。是而本研究以巴西為舞台，從美國－巴西互動、中國－巴西互動，討論新興大國中國與既存支配強權美國間權力轉移的過程，從三方來往間探討權力轉移的跡象並驗證權力轉移論者的主張與假設，另外，本研究嘗試補充權力轉移論者中較少著墨的第三國－區域領導國家，在既存、新興兩強發生權力轉移時所扮演的角色與考量。 / After 2003 Iraq War and financial crisis, the power of dominator, United States is on the way fading. Meanwhile, on the other side of the pacific comes an emerging challenger -China. U.S. decline and China rise complete power transition theory as to illustrate the process of dynamic power change between dominated country and potential challenger. Power transition theory discusses that the war along with power shifting from dominanted state to potential challenger may explore while fulfilling two variables, power parity as the opportunity and negative evaluations of the status quo as the willingness. However, the world politics is well effected by regional countries even on the interactions between two major agents in power transition. Latin America is traditionally regarded as “backyard” of the U.S. but with increased cooperation from China, this claim has been slack. Among all countries in Latin America, Brazil devotees in leading the region due to its rich natural resources and political-economic influence. This article focuses on Brazil and imply competitions between the U.S. and China on the interactions with Brazil so to discuss the power transition phenomena and relevant hypothesis verifications. Furthermore, it tends to develop the autonomy and active position of third state while participating in power transition.