| Named By: | T. D. A. Cockerell in 1906 |
| Time Period: | Late Eocene |
| Location: | USA, Colorado - Florissant Formation |
| Size: | 9.5 millimetres long |
| Diet: | Insectivore |
| Fossil(s): | Partial remains of a female |
| Classification: | | Arthropoda | Insecta | Hymenoptera | Stephanidae | |
Protostephanus is an extinct genus of crown wasp in the Hymenoptera family Stephanidae known from an Eocene fossil found in the United States of America. The genus contains a single described species, Protostephanus ashmeadi placed in the stephanid subfamily Stephaninae.