Vai. Mu. Kothainayaki Ammal
- Birth Date
- 12/1/1901 - 2/20/1960
- Birth Place
- Nirvalur, Chingleput, Tamil Nadu, India
- Known For
- Writing
Vaithamanithi Mudumbai Kothainayaki Ammal (1 December 1901 – 20 February 1960), familiarly known as Vai Mu Ko, was a Tamil writer, novelist, and journalist who was the first woman to occupy the editorial board of a Tamil magazine. She wrote 115 books and published a monthly Tamil magazine, Jaganmohini.