Antibiotic resistance causes public health problems and stimulates research for novel antimicrobials. Particular attention is given to molecules that limit drug resistance development.1 Hen egg white lysozyme acting on the bacterial cell envelope through its physico-chemical properties is thus a good candidate.2,3 However, its antimicrobial effect caused by membrane permeabilization on Gram-negative bacteria remains limited. But some physico-chemical modifications of the lysozyme can modify its membrane activity, increasing lysozyme antimicrobial properties against E. coli; dry-heating is able to induce such modifications.4 Especially, we previously highlighted that native (N-L) and dry-heated lysozyme (DH-L) disrupt the outer membrane of E. coli, but in different ways.3,4 The mode of insertion into the bacterial outer membrane and molecular interactions remains unknown. This was thus investigated using an E. coli lipopolysaccharide monolayer (LPSM) membrane model, mimicking the outer leaflet of the bacterial outer membrane. The interactions between lysozyme and LPSM were studied by tensiometry, ellipsometry, atomic force microscopy (AFM) and Brewster angle microscopy (BAM). Both N-L and DH-L are able to insert into a LPSM. As expected, electrostatic interactions between the negatively charged LPSM and both positively charged forms of lysozyme were observed. Furthermore, we could establish that NL and DH-L insertion into the LPSM depends on the presence of the polysaccharide moieties. These polysaccharide chains might increase the space between the lipid headgroups, enabling lysozyme insertion. Moreover, dry-heating increases the lysozyme affinity for the LPSM. Microscopic observations (BAM and AFM) show that the LPSM reorganizes and reorients in the presence of DH-L, in contrast to N-L. Dry-heating thus improves the lysozyme insertion, which might explain the increased activity on the outer membrane of E. coli, resulting in a higher antimicrobial effect.