Chitosan is a natural biopolymer, a common constituent in exoskeleton of shrimps, crustaceans,insects and fungal cell walls.We investigated the effect of chitosan on the fungal growth inhibition in Lady’s slipper orchid. Peroxidase (POD) and chitinase (CTN) activity were measured in leaf extracts from orchid treated with chitosans ; Fang, Nangfa, Krang, Hunu, Nangrom and Kaching mushrooms (75.43,64.57, 82.86, 88.00, 64.00 and 81.14 %DD respectively). The result showed the highest POD activity(5.85ด 1 0 - 4 Unit/mg) in orchid treated with Fang mushroom chitosan for 2 weeks. However,the highest CTN activity (8.59ด 1 0 - 2 mmol/min/mg) in orchid treated with Nangfa mushroom chitosan for 4 weeks. Orchid resistance to 3 species of fungi (Fusarium moniliforme,Curvularia spp., Phytopthora spp.) were tested in both fungal culture and on the leaves of chitosan treated orchid.The results showed slightly positive effect against those fungi.