彼得大帝之前的俄羅斯是一個典型封閉式的內陸國家，擁有自己的歷史與文化，然而缺乏對外關係的經營與維持。身為一個橫跨歐亞兩洲地區的王國，本身即有充沛的發展潛力得以發展為一個龐大帝國。在彼得大帝正式成為俄羅斯沙皇之後，藉著大使團遊歐之行，並發起諸多層幅深遠的國內改革，最終成功使國家步入西方化，在十八世紀初期躋身歐洲列強之一，為俄國往後的發展開闢了一條嶄新的道路。 　　十八世紀末期是另一段俄羅斯帝國光輝的國家發展史，彼得大帝與凱薩琳大帝統治時期之間，俄羅斯經歷了一段三十餘年的中衰時期，羅曼諾夫王朝子嗣在此時期中斷。凱薩琳大帝繼任俄國沙皇後，將俄羅斯國土面積向西與向南繼續推進，兼併鄰國並在對外戰爭中多次獲得勝利。除了顯赫的領土擴張成果，這位開明君主採取了成功的外交模式而促成國家強權的興起，是俄國歷史上具有承先啟後地位的一位女皇。 　　綜觀俄羅斯歷史，在羅曼諾夫王朝的沙皇當中，只有彼得一世與凱薩琳二世被賦以「大帝」美名，主因是兩位沙皇任內對國家領土大幅擴張，以及提升國際地位能見度的努力與成果。本文除了著重於對兩位君王的分別介紹之外，在沙皇的生長背景與人格特質、國內改革因素探討、國際局勢與對外關係途徑、及領土擴張成果等層面皆做出比較研究，並以研究結果具體總結彼得大帝與凱薩琳大帝的功業，以及留予後世的傳承。 / Russia was an inner-continental country before Peter I’s reign. With its own history and culture context, the empire lacked both operation and maintenance of external relations. From 1689, Peter the Great was formally on the throne, soon he started to westernize his fatherland by any means, and attained fruitful achievements in the beginning of 18th century. It wasn’t until the reign of Catherine the Great in the mid-1700s that Russia was finally able to inaugurate a new policy of Russian southward expansion directly targeting Crimea. Russo-Turkish wars for twice, the partitions of Poland for three times boosted her fame while in reign. The empress also adopted the rule of Enlightenment from France as her main characteristic in domination. This thesis gives a thoroughly introduction to Peter the Great and Catherine the Great as its first part; in the second, there is one comparative study targeting to several fields- from background and personal traits, internal reform, international situation and external relation, to territorial expansion. In sum, what matters are what the Tsars achieved during their regimes respectively, and what they left for posterity.