Objective To explore the differential expression of protein in the serum of individuals susceptible to noise induced hearing loss (NIHL) susceptible individuals working in the military tunnel.Methods A total of 40 soldiers from one tunnel construction troop were divided into the susceptible group and the nonsusceptible group.Twenty soldiers were selected for each group.The average age of the susceptible group was 24.79±2.03 years old and their thresholds of the speech and high frequencies were 22.43±8.31 dB HL and 48.55± 11.54 dB HL,respectively.The average age of the nonsusceptible group was 23.67 ± 3.56 years old and their thresholds of the speech and high frequencies were 13.40±4.13 dB HL and 9.40±2.54 dB HL,respectively.Five microliter peripheral venous blood samples were collected from each individual Two-dimensional electrophoresis (2-DE) and MALDI-TOF-MS were used to separate and identify the differentially expressed proteins.Results Thirty-seven protein spots differentially expressing between the NIHL susceptible and nonsusceptible were found after 2 DE.Compared by mascort score,10 differential proteins were harvested.Among these,5 peptides including proteasome subunit alpha-5,complement C4-A,haptoglobin,apolipoprotein A-I and vitronectin were upregulated,and other 5 ones,including Lysozyme C,beta-2 glycoprotein-1,pigment epithelium derived factor,35 kDa trypsin inhibitor heavy chain H and transthyretin were downregulated in NIHL susceptible individuals.The differences were statistically significant(P＜0.05).Conclusion The differentially expressed proteins were closely related to oxidative stress responses in susceptible individuals,including proteasome subunit alpha-5,complement C4A,haptoglobin,apolipoprotein A-I,beta-2 glycoprotein-1,pigment epithelium derived factor,35 kDa trypsin inhibitor heavy chain H and transthyretin.They might participate in the occurrence of NIHL through this way.The proteins harvested from this study were expected to be specific candidate serum NIHL susceptibility biomarkers in blood to help screen susceptible individuals.