The Prashna Upanishad (Sanskrit: प्रश्नोपनिषद्, IAST: Praśnopaniṣad) is an ancient Sanskrit text, embedded inside Atharva Veda, ascribed to Pippalada sakha of Vedic scholars. It is a Mukhya (primary) Upanishad, and is listed as number 4 in the Muktika canon of 108 Upanishads of Hinduism.

The Prashna Upanishad contains six Prashna (questions), with each chapter discussing the answers. The chapters end with the phrase, prasnaprativakanam, which literally means, "thus ends the answer to the question". In some manuscripts discovered in India, the Upanishad is divided into three Adhyayas (chapters) with a total of six Kandikas (कण्डिका, short sections).

The first three questions are profound metaphysical questions but, states Eduard Roer, do not contain any defined, philosophical answers, are mostly embellished mythology and symbolism. The first question gives a detailed philosophical and logical idea about the origin of life on earth and the description is one of the earliest concepts on Matter and energy. The fourth section, in contrast, contains substantial philosophy. The last two sections discuss the symbol Om and concept of Moksha. Roer as well as Weber suggest that the last two Prashnas may be spurious, later age insertion into the original Upanishad.

Prashna Upanishad is notable for its structure and sociological insights into the education process in ancient India. In some historic Indian literature and commentaries, it is also called Shat Prasna Upanishad.

Prashna (प्रश्न) literally means, in modern usage, "question, query, inquiry". In ancient and medieval era Indian texts, the word had two additional context-dependent meanings: "task, lesson" and "short section or paragraph", with former common in Vedic recitations. In Prashna Upanishad, all these contextual roots are relevant. The text consists of questions with lessons or answers, and the sections within the Upanishad are also called prashna.

The Prashna Upanishad was probably composed in the second half of 1st millennium BCE, likely after other Atharva Veda texts such as the Mundaka Upanishad, but the precise chronology of Prasna Upanishad is unclear and contested. The Mundaka Upanishad, for example, writes Patrick Olivelle, is rather later era ancient Upanishad and is, in all probability, post-Buddhist. The chronology of Prasna Upanishad, and other ancient India texts, is difficult to resolve because all opinions rest on scanty evidence, an analysis of archaism, style and repetitions across texts, driven by assumptions about likely evolution of ideas, and on presumptions about which philosophy might have influenced which other Indian philosophies.

Olivelle states Prashna Upanishad "cannot be much older than the beginning of the common era". Mahony suggests an earlier date, placing Prashna along with Maitri and Mandukya Upanishads, as texts that probably emerged about early fourth century BCE. Phillips dates Prashna Upanishad as having been composed after Brihadaranyaka, Chandogya, Isha, Taittiriya and Aitareya, Kena Katha and Mundaka, but before Mandukya, Svetasvatara and Maitri Upanishads. Ranade posits a view similar to Phillips, with a slightly different ordering, placing the Prashna Upanishad's chronological composition in the fifth group of ancient Upanishads, but after the Svetasvatara Upanishad.

The Prashna Upanishad consists of six questions and their answers. Except the first and the last Prashna, all other sections ask multiple questions. The pupils credited with the six questions are respectively Kabandhin Katyayana, Bhargava Vaidarbhi, Kausalya Asvalayana, Sauryayanin Gargya, Saibya Satyakama and Sukesan Bharadvaja. Sage Pippalada is credited with giving the answers.