Otto Pfleiderer (September 1, 1839 - July 28, 1908), was a German Protestant theologian.

He was born at Stetten near Cannstadt in Württemberg. From 1857 to 1861 he studied at the University of Tübingen under FC Baur, and afterwards in England and Scotland. He then entered the ministry, became "repetent" at Tübingen, and for a short time held a pastorate at Heilbronn (1868). In 1870 he became chief pastor and superintendent at the University of Jena and soon afterwards professor ordinarius of theology, but in 1875 he was called to the chair of systematic theology at Berlin, having made his name by a series of articles on New Testament criticism and Johannine and Pauline theology, which appeared in Adolf Hilgenfeld's Zeitschrift für wissenschaftliche Theologie, and by his Der Paulinismus, published in 1873 (Eng. trans., Paulinism: a Contribution to the History of Primitive Christian Theology, 2 vols., 1873, etc.). Das Urchristentum, seine Schriften und Lehren, in geschichtlichen Zusammenhang beschrieben was published in 1878 and considerably enlarged for a second edition in 1902 (Eng. trans., 1906).

In 1890 appeared The Development of Theology since Kant, and its Progress in Great Britain since 1825, which was written for publication in England. A more elaborate work was his Religionsphilosophie auf geschichtlichen Grundlage (1878; Eng. trans., from 2nd German ed., The Philosophy of Religion on the Basis of its History, 4 vols., 1886—1888). "The Influence of the Apostle Paul on the Development of Christianity" was the title of a course of Hibbert Lectures given in London in 1885. In 1894 he delivered the Gifford Lectures at Edinburgh, the subject being "The Philosophy and Development of Religion." His later publications included:

• The Early Christian Conception of Christ (1905)
• Die Entstehung des Christentums (1905; Eng. trans., 1906)
• Religion und Religionen (1906; Eng. trans., 1907)
• Die Entwicklung des Christentums (1907).

He died at Gross Lichterfelde, near Berlin. In New Testament criticism Pfleiderer belonged to the critical school which grew out of the impulse given by FC Baur. But, like other modern German theologians, he showed a greater disposition to compromise. All his work shows a judicial tone of mind, and is remarkable for the charm of its style.