Oskar Kraus (24 July 1872 – 26 September 1942) was a Czech philosopher and jurist.

Oskar Kraus, who converted from the Jewish to the Protestant faith, was born in Prague, the son of Hermann Kraus and Clara Reitler-Eidlitz. In 1899 he married Bertha Chitz.

In 1890 he began to study jurisprudence and philosophy under Friedrich Jodl and Anton Marty, who introduced him into Franz Brentano's philosophy. Kraus made his Doctor of Philosophy in 1895 and attained the habilitation in philosophy in 1902. In 1909 he became Professor extraordinarius and in 1916 Professor ordinarius. After the Germans occupied Czechoslovakia in 1939, Kraus was put into an concentration camp; however, after he was released he fled to Great Britain. At the University Edinburgh he held Gifford Lectures in 1941. In 1942 he died, aged 70, in Oxford, of cancer.

During World War I, Kraus worked on topics in relation to war and ethics and wrote important works in the field of public international law.

Influenced by Brentano, Kraus developed an a priori value theory, which was formulated in opposition to Marxian value theory. He also applied this method on economics.

Based on his ideas on law and duty he developed a juristic hermeneutics in the field of jurisprudence, and criticized historism and positivism.

Kraus was also known for his criticism of the theory of relativity, which was according to him an accumulation of "absurdities" (like the constancy of the speed of light) and "mathematical fictions".