In this study, the effect of repeated foliar treatments of Harpin Protein on the yield and fruit quality of pepper grown in greenhouse conditions was investigated. The messenger was used as a commercial product of Harpin Protein and the application rate was 50 g / 100 L water commercial product. First applications were done on the seedlings in 3 leaf stages and the applications were repeated at 14 day intervals for three applications. At the end of the study, it was determined that the messenger applications increased the total yield of pepper cultivars named 'Ilica 256', 'Demre', 'Sari Sivri' and 'Yalova Charleston'; 16%, 15.7%, 5.4% and 11.5%, respectively. Treatments of Harpin Protein have also had positive effects on some fruit quality parameters such as soluble solids, titratable acidity and pH.