Four Schiff bases, L1, L2, L3 and L4 having –ON– donor system have been synthesised by the condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 4-nitrobenzohydrazide and 4-methoxybenzohydrazide to form L1 and L2. 4-(dimethylamino) benzaldehyde refluxed in the presence of 4-nitrobenzohydrazide and 4-methoxybenzohydrazide forms L3 and L4, respectively. The four Schiff base complexes (SBC 1A–1D) were synthesised by treatment of the Schiff base ligands with vanadium acetylacetonate and characterised using spectroscopic analysis such as FTIR revealing the presence of azomethine μ (C=N) stretching vibrations around 1612–1623 cm−1, 1H and 13C NMR revealing the presence of azomethine peaks to confirm the formation of the Schiff base ligands. The spectral data of the Schiff base complexes reveal the absence of the azomethine stretching vibrational frequencies and the presence of the V–O stretching vibrational frequency at 993 cm−1. Thermal analysis of the ligands and complexes indicates high thermal stability of 280 and 160°C, respectively. Schiff base complexes 1A and 1B exhibited antimicrobial activities against both species tested with MIC of 305.3 and 378.9 mg/mL, these activities were dependent on the position of the hydroxyl and the length of the alkyl groups on the 4-Methoxy-benzoic acid (4-diethylamino-2-hydroxy-benzylidene)-hydrazide moiety of the Schiff bases complex.