Mango cv. Nam Dok Mai is an important economic fruit of Thailand. However, it always has a problem
from anthracnose caused by Colletotrichum gloeosporioides. Use of chemical control may cause the remaining
recidure. Chitosan at 0.1, 0.5, 1.0, 1.5 and 2.0%, compared with 750 ppm (0.075%) benomyl and sterile distilled
water were mixed to Potato Dextrose Agar (PDA) tested with  C.gloeosporioides in vitro by poisoned food
technique, mycelium disc of C. gloeosporioides was old 7 days on PDA mixed with chitosan.  This was put center
of the agar plate. Incubation temperature at 25 oC. Mycelium growth was recorded by measuring the diameter of
mycelium growth for 7 days. The result demonstrated that 2.0 % chitosan inhibited 80.4 % of mycelium growth
80.4 % while 0.075 % benomyl and sterile distilled water inhibited the mycelium at 100.0% and 0.0% respectively.  
Keywords: Chitosan, Mango Fruit cv. Nam Dok Mai, C. gloeosporioides