Bawang Dayak (Eleutherine americana Merr. Ex K. Heyne) is one of Indonesian herbal plant that were used as traditional medicine. Bulbs of the plant were examined and contain many of bioactive compounds. The objective of this reseach was to investigated the antimitotic activity of red bulb extract by using onion meristematic index method. The extraction was done by soxhletation method using ethanol. Results shows that red bulb extract has antimitotic activitiy. It was shown by chromosome duplication on onion mitotic cells, from 2n=16 to 4n=32. On the concentration extract of 0.01%, an optimal antimitotic activity was observed. This finding may valuable information for initial discovering of polyploidization agent in Indonesia.