Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be observed by electron microscopy. It refers in general to the study of cellular structures that are too small to be seen with an optical microscope. The term is also sometimes spelled Ultra-Structure.

Ultra-Structure is also the name given to a notational system for representing complex rules (see Long, J., and Denning, D., Ultra-Structure: A design theory for complex systems and processes. In Communications of the ACM (January 1995)

Ultrastructure