The main feature of Heideger's philosophy is its monistic character. The terms Being, nothingness, time, metaphysics we face in Heidegger's philosophy are various terminological aspects of the same ontological problem. His masterpiece which is specified to understand "Being" only is Being and Time. In this work, Heidegger deals with and tries to understand the problem of being in scrutiny but in a different way from the previous philosophies. The other term which cannot be separated from being is nothingness. Heidegger goes through in detail the problem of nothingness in his published lecture called What is Metaphysics? However we believe that the terminological background of analysis carried out in What is Metaphysics? is mostly in Being and Time. In this paper, Heidegger's analysis of nothingness will be studied in the context of analysis of being in Being and Time.