According to theism, God is that ultimate being who does not have a beginning or an end, which has created this universe and has all the powers to sustain it. The existence of God has always been a topic of debate in philosophy as many philosophers have proposed their own arguments which either support or reject the idea that God exists. The difference in thoughts arises because there is difference in the perception about God. The definition of God, proof, knowledge differs from person to person. Therefore, not only does the question “What is God?” affects the opinion of people, also the different opinion regarding what should be considered as proof to prove an argument is also responsible for having different opinions on existence of God (Sobel, 2004). The objective of this paper is to analyze the cosmological arguments given by a famous philosopher, Thomas Aquinas, and bring out the objections and criticism it went through by other scientist, thus evaluating whether the argument is sound and logical in proving the existence of God.