| Margaret Ensign Lewis | |
| Birth Date: | 1919 |
| Death Date: | November 2017 |
| Alma Mater: | Pomona College (undergraduate), University of California, Berkeley (master's) |
| Workplaces: | Amherst College, University of California at Los Angeles Herbarium |
| Spouse: | Harlan Lewis |
Margaret Ruth Ensign Lewis (1919 – November 2017) was an American botanist, taxonomist, and professor specializing in California flora.
The International Plant Names Index lists 38 plant names published by Margaret Ruth Ensign.