Abstract： Objective To observe the expression of triggering receptor-1 on myeloid cells (TREM-1) of mice with acute lung injury (ALI) in oder to find out its regularity and significance in inflammatory response of or-ganisms. Method Thirty BALB/C mice were randomly(random number) divided into normal control group (n =6) and ALl group (n = 24). The models of ALI were made with intraperitonal injection of lipopolysaccharide (LPS) in dose of 10 mg/kg. Specimens from peripheral blood and lung tissue were collected 6 h, 12 h, 24 h and 48 h after LPS injected. The fluorescent real-time quantitative reverse transcriptiun-polymerase chain (RT-PCR) was used to detect TREM-1 mRNA, and ELISA was employed for detection of TREM-1 protein and TNF-α protein, and HE staining was made doe the pathological Smith lung score under light microscope. Analysis of variance was used for comparison of TREM-1 mRNA, TNF-α and Smith lung injury score between two groups. Spearman corre-lation analysis was made to find out the relationship among these three variables. Results The expressions of TREM-1 mRNA in lung tissue of ALI mice 6 h, 12 h, 24 h, and 48 hours after injection of LPS were 6.61±0.08,34.71±0.83, 61.85±14.05 and 56.46±8.89, respectively which were higher than that in control group (1.00±0.00, P = 0.017, 0.009, 0.002 and 0.003, respectively). The expressions of TREM-1 mRNA in blood were 14.01±3.24, 47.07±0.98, 8.18±0.43 and 8.06±0.05, respectively which were higher than that in normal control group (1.00±0.00, P = 0.010, 0.004, 0.011 and 0.011, respectively). The expression of TREM-1 rnRNA in tissue began to increase 6 hours after modeling and reached its peak 24 hours later, and expres-sion of TREM-1 mRNA in blood reached its peak after 12 hours. The levels of TREM-1 protein in lung tissue of ALl mice 6 h,12 h,24 h and 48 hours after LPS injected were 997.8±114.62, 1579.70±45.92, 1123.9±108.2 and 429.8±89.96 pg/mL, respectively which were higher than that of mice in control group (279.22±4.62 pg/mL, P = 0.024, 0.007, 0.011 and 0.04, respectively). The level of TREM- 1 protein reached the peak 12 hours after LPS injected, but it had no significant correlation with the expression of TREM-1 mRNA (P =0.14). The levels of TNF-α protein in lung tissue of ALI mice 6 h, 12 h, 24 h and 48 hours after LPS injection were 313.16±39.50, 491.91±96.65, 388.48±29.84 and 282.5±52.76 pg/mL, respectively which were sig-nificantly higher than that of mice in control group (256.6±28.31 pg,/mL, P = 0.037, 0.019, 0.032 and 0.043, respectively). The TNF-α concentration was positively correlated with TREM-1 levels in lung tissue and with Smith pathological score (r = 0.795, P = 0.001: r = 0.499, P = 0.034), but not with the expression of TREM-1 mRNA (P = 0.176). Conclusions The expression of TREM-1 mRNA in lung tissue of mice with ALI is elevated, and the expression of TREM-1 mRNA is related to the level of TNF-α and the severity of the ALI in in-flammatory responses in lung. The expressions of TREM- 1 gene are not consistent with the levels of TREM- 1 pro-tein, suggesting another new functional proteins involved in immune regulation.