Ka'ba-ye Zartosht (Persian: کعبه زرتشت), also called the Cube of Zoroaster, is a rectangular stepped stone structure in the Naqsh-e Rustam compound beside Zangiabad village in Marvdasht county in Fars, Iran. The Naqsh-e Rustam compound also incorporates memorials of the Elamites, the Achaemenids and the Sasanians.

The Ka'ba-ye Zartosht is 46 metres (151 ft) from the mountain, situated exactly opposite Darius II's mausoleum. It is rectangular and has only one entrance door. The material of the structure is white limestone. It is about 12 metres (39 ft) high, or 14.12 metres (46.3 ft) if including the triple stairs, and each side of its base is about 7.30 metres (24.0 ft) long. Its entrance door leads to the chamber inside via a thirty-stair stone stairway. The stone pieces are rectangular and are simply placed on top of each other, without the use of mortar; the sizes of the stones varies from 0.48 by 2.10 by 2.90 metres (1 ft 7 in by 6 ft 11 in by 9 ft 6 in) to 0.56 by 1.08 by 1.10 metres (1 ft 10 in by 3 ft 7 in by 3 ft 7 in), and they are connected to each other by dovetail joints.