Abstract: Twenty-five candidate MLO genes of Lonicera japonica were obtained by whole genome sequencing. Bioinformatics analysis showed that the number of amino acids in the protein family ranged from 137 to 846, the theoretical isoelectric point ranged from 5.02 to 9.50, and it was rich in basic amino acids. One protein did not contain transmembrane domain, and the other proteins ranged from 3 to 10. The results of subcellular localization showed that 21 proteins were located on the cell membrane and 1 protein was located on the chloroplast. Phylogenetic trees were constructed from 133 MLO proteins of Lonicera japonica, Triticum aestivum, Arabidopsis thaliana, Solanum lycopersicum, Nicotiana tabacum, Nicotiana sylvestris and Nicotiana tomentosiformis. The results indicated that MLO family proteins of Lonicera japonica could be divided into five subgroups. Tissue specific analysis showed that the expression of MLO genes in Lonicera japonica had obvious tissue specificity. Among them, 8 genes were highly expressed in leaves, 2 genes in stems and 2 genes in flowers. Four genes were significantly upregulated after inoculation with powdery mildew, among which MLO14 increased the most, which was more than 2 000 times higher than that of the control. In this study, the composition and expression of the MLO gene related to the occurrence of powdery mildew of Lonicera japonica were preliminarily analyzed, which laid a foundation for the further use of MLO as a target gene to develop new germplasm resistant to powdery mildew of Lonicera japonica.