A successful application of humic acids and diazotrophic bacteria in corn represents a potential that collaborates to break the current energetic consumption paradigm, which is based on unsustainable fossil sources. Thus, this study aimed to quantify the contribution of diazotrophic bacteria in association with humic acids and nitrogen (N) in corn, in an experiment conducted under controlled conditions in a greenhouse. The experiment was carried out at the Federal Institute of Rondonia, Campus of Colorado do Oeste-RO, Brazil. The experimental design was completely randomized with four replicates and the treatments consisted of: control; inoculation of Azospirillum brasilense; 80 kg ha-1 of N; inoculation of A. brasilense + humic acid; inoculation of A. brasilense + 80 kg ha-1 of N; and inoculation of A. brasilense + 80 kg ha-1 of N + humic acid. At 40 days after emergence, plants were collected, divided into shoots and roots, and the variables were analyzed. According to the results, the joint use of plant growth-promoting bacteria and humic acids increased in plant height, stem diameter and root length and volume. Inoculation of A. brasilense combined with 80 kg ha-1 of N and humic acid increased N use efficiency in corn plants by 60%, while inoculation of A. brasilense combined with 80 kg ha-1 of N increased shoot N contents in corn plants. Key words: Zea mays L., Azospirillum brasilense, humic substances, biological nitrogen fixation (BNF).