The effects of diazotrophic bacteria inoculation associated to phosphate fertilization on plant growth and leaf gas exchange parameters in maize plants (Zea mays L.) were investigated in the present study. Maize plants were grown in 13-L pots filled with clayey Rhodic Hapludox in a greenhouse. Treatments were arranged in a randomized block design in a 4 × 2 factorial: four seed inoculation treatments [control (non-inoculated); inoculation with Azospirillum brasilense strain AbV5; inoculation with Herbaspirillum seropedicae strain SmR1; and inoculation with two bacteria strains (A. brasiliense + H. seropedicae)] and two phosphate fertilization levels [no fertilized or fertilized with phosphorus (300 mg dm–3 of P2O5)]. Phosphorus fertilization resulted in higher plant height, stem diameter, number of leaves per plant, leaf area, dry matter yield of leaves, stems and sheaths of maize plants, regardless of seed inoculation with diazotrophic bacteria. Seed inoculation with A. brasilense and H. seropedicae increased in 42% of the volume root, in 52% of the root dry matter and 25% of the plant height of maize, indicating an increase in the phosphorus solubilization or higher phosphorus use provided by the maize root system. Seed inoculation with A. brasilense associated to phosphorus fertilization increased in 23% of the relative chlorophyll content, resulting in higher metabolic structure to the photosynthetic activity of maize plants. The leaf CO2 assimilation rate was not affected by the phosphorus fertilization and maize seed inoculation with A. brasilense and H. seropedicae. Key words: Plant growth promoting bacteria, phosphate solubilization, gas exchange, Azospirillum brasilense, Herbaspirillum seropedicae, Zea mays.