The Meng-Yin or Mengyin Formation (simplified Chinese: 蒙阴组; traditional Chinese: 蒙陰組; pinyin: Méngyīn Zǔ) is a geological formation in Shandong, China, whose strata date back to the Berriasian and Valanginian stages of the Early Cretaceous.

[1][2] Dinosaur remains are among the fossils that have been recovered from the formation.

[3] The type material for the titanosauriform dinosaur Euhelopus was excavated at this formation by Otto Zdansky in 1923, in green/yellow sandstone and green/yellow siltstone that were deposited during the Barremian or Aptian stages of the Cretaceous period, approximately 129 to 113 million years ago.

[4] Both the genus and species of Mengyinaia mengyinensis were named after the formation.

Indeterminate stegosaurid remains have been found in Shandong, China.