C. J. Quandt was a German piano manufacturer founded in Berlin in 1854 by Carl Julius Quandt (1817–1896). Operating as a Hof-Pianofortefabrik (Royal Court Piano Factory), the firm was based at Grüner Weg 55 and later expanded into adjoining premises as demand grew. Quandt had trained as a carpenter and worked at piano houses including A. Pfeiffer in Glogau, B. Voigt, and Gottfried Perau before starting his own workshop.

The company built upright and grand pianos, with several technical innovations attributed to the family and its partners. Carl's son Emil Quandt patented the "Quandt soundboard" (D.R.P. 115,486), a radially-arranged laminated design intended to improve tone, and partner Max Baum developed a patented mechanism allowing smoother transitions between normal and soft playing dynamics.

C. J. Quandt held the title of Hoflieferant (official court supplier) to the Hohenzollern royal family and earned recognition at various European exhibitions, including the 1906 Berlin music trade show. The firm produced roughly 24,000 instruments over the course of its operation, and surviving uprights from the late 19th and early 20th centuries still circulate in the antique piano market.

C. J. Quandt has 1 product cataloged on Equipboard, including Upright Pianos.