We investigated the corrosion behavior of 5754 aluminium alloy in metalcutting fluid (MCF) containing P. pseudoalcaligenes which was isolated from a waste metalcutting fluid (WMCF). The single strain was purified and isolated by streak plate method and sequenced using 16S rDNA. P. pseudoalcaligenes was inoculated into the MCF and 5754 aluminium alloy specimen were immersed in the bio-contaminated MCF simultaneously. pH, emulsion droplets size distribution, dissolved oxygen, TOC, IC, and TN in the MCF were investigated to analysis the biodeterioration of MCF under the influence of P. pseudoalcaligenes. The microbially influenced corrosion behavior of 5754 aluminium alloy in the MCF was characterized by morphological characterization of metal and the attachment of biofilm. The polarization curves and EIS were applied to analyze the electrochemical behavior of aluminium alloy in the MCF containing P. pseudoalcaligenes. Remarkable growth of P. pseudoalcaligenes was showed in the MCF and the biomass remained at 107 CFU/mL. A severe biodegradation of MCF was observed, with the pH decreased from 9.25 to 7.39 and the curve of emulsion droplets size distribution transforming into bimodal (1.12 μm, 8.93 μm) from monomodal (1.07 μm). The coalescence between emulsion droplets was observed after the staining of droplets. The change of TOC and TN showed a decline from 15.42 g/L and 564.77 mg/L into 9.69 g/L and 142.16 mg/L, respectively. And the increase of IC was obtained during the biodegradation. A biofilm was occurred on the surface of 5754 aluminium alloy immersed in MCF containing P. pseudoalcaligenes for 10 days and a seriously pitting was observed in the matrix under the biofilm after immersion for 15 days. Results of polarization curve showed that the Ecorr shifted negatively under the microbial influence. The Jcorr of aluminium alloy immersed in MCF with microbes for 15 days increased from 0.274 μA/cm2 to 0.477 μA/cm2. The Jcorr of aluminium alloy immersed in bio-contaminated MCF for 15 days was 4.9-fold greater than in the absence of bacteria. The pitting was easily occurred on the surface of metal due to the negative shift of pitting potential. Result of EIS presented that the semidiameter of impedance was decreased with the extension of immersion time. The resistance of corrosion of 5754 aluminium alloy was weakened under the presence of P. pseudoalcaligenes. P. pseudoalcaligenes preferentially degraded the nitrogen-containing organic compounds such as buffer and emulsifier into soluble inorganic salts, which reduced the pH value of cutting fluid and the protective effect of emulsifier and increases the conductivity of solution, making the deteriorated cutting fluid more corrosive. The aluminium alloy showed more corrosive in an aggressive media. Oxygen was almost consumed by bacteria in the biofilm. The passivating film of Al2O3 was incomplete to protect matrix due to the lack of oxygen which led to the pitting under the biofilm.