The effects of harpin protein and fermentation product of Lactobacillus acidophilus (LaFü- be-mm), which were known as plant defence activators, were investigated under pot conditions on grey mould disease on lettuce caused by Botyrtis cinerea Pers.: Fr., in this study. A fungicide with active ingredient fenhexamide for comparison and two lettuce cultivars Chianti and Yedikule were used through the experiments. Plant activator applications were carried out at interval of fourteen days with five times using hand spray. After the third application, spore suspension of pathogen (1x105 spore/ml) was inoculated to the leaves of the plants. Harpin protein application reduced the disease incidence on cultivars Chianti and Yedikule at the rates of 57.50% and 68.75%; LaFü-be-mm at the rates of 30% and 57.50% respectively. Fenhexamid application had the highest effectiveness on both cultivars (90% and 92.50% for Chianti and Yedikule, respectively). However, there were statistically differences between activator applications and control treatment for disease incidence on both cultivars. This study suggests promising results obtained with application of two activators to prevent grey mould disease in lettuce.