The idea of utopia originally came from Thomas More's Utopia. Utopian literature is mainly concerned with social systems such as politics, laws, and customs. In an utopia, descriptions of imaginary remote regions in an ideally perfect condition can be found. The setting of Jonathan Swift's Gulliver's Travels is imaginary, distant countries. In addition, Swift makes ambiguous the distinction between the imaginary world and the real world. This is one of the attractive points of Swift's work. Gulliver's Travels is both a mock-traveller's tale and an imaginary voyage. Presenting an ideal condition in this work was not Swift's intent. But there certainly exist some utopian elements in the original Institution of Lilliput. The description of Lilliputian social systems is related to utopian literature because it is written as if it were a treatise, not an ordinary narrative. Brobdingnag also can be regarded as an utopian country that consists with a very simple culture, in contrast to the abuse of the European civilization. However, an utopia can easily turn into a dystopia. In other words, what is utopia to one reader can be seen as a dystopia to another. Any judgment whether a certain society depicted in utopian fiction is an utopia or a dystopia must be arbitrary. As an example, we can point out the matter of freedom of speech that is mentioned by the King of Brobdingnag. He does not allow his subjects to express their opinion without any restriction. Thus the country cannot be regarded as a pure utopia. Any interpretation of Gulliver's Travels is inevitably a complicated one since this book is a mock-utopia that parodies the whole idea of utopia and mocks the utopian mentality. Religious systems, including freedom of religion, are contemplated seriously in More's Utopia. On the other hand, freedom of speech is satirised in the Voyage to Brobdingnag and again in the Voyage to the Country of the Houyhnhnms. Even the existence of opinion is unknown among the horses. It is not sufficient to consider Houyhnhnmland as a typical dystopia. The world described in the fourth voyage is so uncanny a world that it makes any discussion to decide whether it is an utopia or a dystopia almost meaningless. This notion is supported by the interpretation that Gulliver-as-narrator, who was instructed by the reason of the Houyhnhnms, is a madman at the end of his travels. Although Gulliver's Travels has both utopian and dystopian elements, the book is neither a work of utopian nor of dystopian literature, but rather a parody of utopia and an extraordinary satire which represents Swift's unique view of the world.