Bell pepper is a vegetable of great socioeconomic importance in the Brazilian market. However, in the semi-arid region of northeast Brazil, its cultivation is limited by the high concentrations of salts in water sources. On this basis, this study was developed to determine the effect of foliar application of hydrogen peroxide in mitigating salt stress by evaluating gas exchange, photosynthetic pigments, and growth in 'All Big' bell pepper plants. The experiment was conducted in greenhouse conditions in Campina Grande - PB, Brazil. Treatments were distributed in a randomized block design with a 5 x 5 factorial arrangement corresponding to five levels of irrigation-water electrical conductivity (ECw: 0.8, 1.2, 2.0, 2.6, and 3.2 dS m-1) and five concentrations of hydrogen peroxide (H2O2: 0, 15, 30, 45, and 60 mu M), with three replicates and one plant per plot. Foliar application of hydrogen peroxide at the concentration of 15 mu M attenuated the effects of salt stress in 'All Big' bell pepper plants irrigated with saline water at ECw of up to 1.4 dS m(-1). Hydrogen peroxide at a concentration of 15 mu M associated with water salinity of 0.8 dS m(-1) increased stomatal conductance, CO2 assimilation rate, instantaneous carboxylation efficiency, and the growth of the bell pepper plants. Application of hydrogen peroxide at concentrations greater than 15 mu M intensified the deleterious effects of salt stress in 'All big' bell pepper at 90 days after sowing.