Abstract: In order to study the defensive role and action mechanism of antibacterial peptide NK-Lysin during body reaction, when pathogen infect animal body. This study detected the expression of NK-Lysin induced by different concentrations of lipopolysaccharide(LPS) and in different immune organs by Real-time fluorescence quantitative PCR, and explored the generation and response of sheep antimicrobial peptide NK-Lysin in immune organs. The cloning vector of target gene NK-Lysin and reference gene GAPDH were constructed, drew the standard curve and detected the expression of NK-Lysin. The results showed that inducing with the LPS concentrations of 0.01, 0.1, 1 and 10 μg/mL, respectively，the expression of NK-Lysin reached the maximum within 8 h. There was no positive correlation between the expression of NK-Lysin and concentration of LPS. The expression of NK-Lysin mRNA had varying degrees in pre-shoulder lymph, spleen and blood. The expression in spleen was extremely significantly different compared with other organs(P＜0.01). Immune organs could express the antimicrobial peptide NK-Lysin in a relatively short time, and NK-Lysin participated in the body’s innate immunes responses.