According to a new regulatory filing, Carl Icahn bought 611,354 shares of Herbalife on May 3.
This increases his stake of the company to 16.48%, up from 15.89%.
Icahn made his big move into Herbalife after hedge fund giant Bill Ackman accused the company of being an illegal pyramid scheme.
Ackman has said his price target for the company is $0.
Herbalife shares are currently up 3% in after-hours trading.