¹College of Animal Science and Technology, Shihezi University, Shihezi, Xinjiang, 832003, PR CHINA DOI : 10.9775/kvfd.2017.18131 Mannose Binding Lectin (MBL) is a liver-derived, circulating plasma protein that plays a pivotal role in innate immunity, however, MBL polymorphisms in sheep were associated with the incidence of MO infection. The objective of this study was to determine the relationships between the different genotypes of MBL and the resistance against MO infection disease, including three hundred and thirty-six individuals of the China Merino sheep. Single-Strand Conformation Polymorphism (SSCP) analyses of PCR amplicons of the exon-1 region of the MBL gene revealed four patterns: BB, BC, CC and DD. However, BB, BC and DD genotype have 3 SNPs, 2 SNPs, and 4 SNPs respectively, and CC genotype has only an identical sequence to the reference, among which there are 3 synonymous SNPs and 6 non-synonymous SNPs. Our statistic analysis showed that the DD genotype MBLs in China Merino sheep were associated with the decrease of MBL protein level in serum. The sheep carrying this kind of genotype were more susceptible to MO infection, however, an opposite result was found in sheep having CC genotype, which will provide a reference for molecular breeding of sheep breeds resistant to MO infection. Keywords : Polymorphisms, China Merino sheep, Mannose-binding lectin, PCR-SSCP, Mycoplasma ovipneumoniae infection