Pepper is quite sensitive to water stress, thus changes in irrigation levels may have significant effects on yield, organic acids and phenolics of peppers. Improper irrigation levels may generate a water stress and resultant stress then create serious oxidative damages on cell membranes. Such damages can be prevented with proline-like antioxidative substances. This study was conducted in Canakkale - Turkey to investigate the effects of different irrigation levels and proline treatments on yields, quality parameters and organic acid composition of pepper (Capsicum annuum L. cv. Yalova Yaglik 28) in the years of 2013 and 2014. Experiments were conducted in randomized blocks split plots experimental design with 3 replications. Three different irrigation levels were arranged as to apply certain percentages of total evaporation from Class-A pan (Kcp(50), Kcp(100), Kcp(150)). Proline treatments (12 mM) were applied at 3 different growth stages (three equal portions on 20, 30 and 40th days, single treatment on 30th day and single treatment on 40th day of growth). In both years of the experiments, decreasing citric acid contents and increasing ascorbic acid contents (in the first year of experiments, Kcp(50)=84.54, Kcp(100)=175.48, Kcp(150)=198.92 mg/100g) were observed with increasing irrigation levels. Different irrigation levels and proline treatments had significant effects on yield (g/m(2)), total phenolics (mg/100g), soluble solids content (SSC, %) and internal proline content (mu mol/g) of pepper fruits. Adversely affected parameters as yield (g/m(2)) and ascorbic acid content due to limited irrigation positively affected with some proline treatments.