This study aimed to (i) select the endophytic bacteria from maize roots for their N2-fixing ability and (ii) evaluate the efficacy of potent indigenous bacterial strains on soil fertility, nitrogen (N) uptake, and growth and yield of maize. A total of 31 maize root samples were collected from An Giang province in Vietnam to isolate the bacteria. The pot experiment was conducted in nine treatments: (i) 100% N of the recommended fertiliser formula (RFF), (ii) 85% N of RFF, (iii) 70% N of RFF, (iv) 55% N of RFF, (v) 85% N of RFF plus a mixture of two potent strains of nitrogen-fixing endophytic bacteria (NFEB), (vi) 70% N of RFF plus a mixture of two potent strains of NFEB, (vii) 25% N of RFF plus a mixture of two potent strains of NFEB, (viii) 0% N of RFF plus a mixture of two potent strains of NFEB, and (ix) 0% N of RFF. The experiment was conducted in the greenhouse to collect soil and plant samples at harvest and observe their growth and agronomic parameters. The results showed that two acid-resistant endophytic bacterial strains were selected and identified as Enterobacter cloacae ASD-21 and E. cloacae ASD-48. At 85% N level, a mixture of the two endophytic bacteria strains was applied as biofertilisers and proved their ability to significantly enhance NH4+ content and N uptake, with an increase of 14.8 mg NH4+ kg-1 and 0.26 g N pot-1, respectively. A mixture of the two potent strains of NFEB produced higher values in plant height, stem diameter, cob length, and cob diameter compared to 100% N of RFF. It replaced 15% N of RFF but still maintained the maize grain yield.