Abstract: Four neem (Azadirchta indica A. Juss) products namely crude neem seed oil, nimbokil, crude neem seed oil terpenoid extract and neem leaf decoction were tested for their in vitro activity against mycelial growth, sporangial germination and sporangial production of Phytophthora infestans. All the products were found highly effective against the different life stages of the fungus. The compounds were evaluated both with and without being heat sterilized along the medium. The heat sterilized compounds were comparatively less effective as compared to the ones which were used without heat sterilization. The results show that neem products have potential for the management of potato late blight disease.