Abstract Ultrathin 2D nanomaterials possess promising properties due to electron confinement within single or a few atom layers. As an emerging class of functional materials, ultrathin 2D rare‐earth nanomaterials may incorporate the unique optical, magnetic, and catalytic behaviors of rare‐earth elements into layers, exhibiting great potential in various applications such as optoelectronics, magnetic devices, transistors, high‐efficiency catalysts, etc. Despite its importance, reviews on ultrathin 2D rare‐earth nanomaterials or related topics are rare and only focus on a certain family of ultrathin 2D rare‐earth nanomaterials. This work is the first comprehensive review in this impressive field, which covers all families of ultrathin 2D rare‐earth nanomaterials, illustrating their compositions, syntheses, and applications. After summarizing the current achievements, the challenges and opportunities of future research on ultrathin 2D rare‐earth nanomaterials are evaluated.