Sanggyu LeeWoolf is a key exemplar of modernist writers who deal with the theme relating to the existential being of 'otherness' and 'madness.' This paper shows how the idea of the 'otherness' of 'madness' is represented in Virginia Woolf's Mrs. Dalloway. We can see how the characteristics of the 'other' of madness are reflected in Mrs. Dalloway through the minor insane character Septimus Smith. Septimus, who suffers from the trauma of shell-shock after coming back from the First World War, is isolated from the dominant authoritarian class and is considered insane. The dominant class tries to label Septimus as a madman in the name of proportion and reason in the male-centered patriarchical times. He is considered socially as the being of the 'other.' We, however, ultimately need to realize that Septimus is also a common English man and lives with his family as a husband. Furthermore, he should be treated as a human being and he needs to be regarded as a victim of the shell-shock of war.Septimus' madness should not be treated as anxiety and despair but as a state of nothingness. Therefore, he gets to experience somewhat paradoxical results in the middle of puting himself into others. Foucault asserts that the dominant authoritarian groups categorize the identity of madness as 'irrational, deficient, and losing.' So, the study of Septimus' madness requires to be approached with attitudes of humanitarian viewpoint and dedicated mind. Even though he seems to be extraordinary 'other' considering his strange words and unimaginable activities, he is now experiencing an intolerable life that the common people can't stand. That's why it is worth while to study the 'other' of madness with a theory of existentialism. Key Wordsother(ness), madness, shell-shock, nothingness, trauma, male-centered patriarchical times