The aim of the present work was to analyse the change of egg white antibacterial activities during egg incubation. Embryonic (E) and unfertilized (U) eggs were incubated for several periods of time, from 0 to 12 days, and the resulting egg whites were analyzed for their pH, protein content and for their antibacterial properties against 5 pathogenic strains. The changes in egg white pH values differed between U and E eggs. Egg white concentrations remained stable during incubation for U eggs but significantly increased for E eggs. At constant protein concentration and for an dentical duration of incubation, egg white activities against Listeria monocytogenes et Streptococcus uberis were similar between E and U groups. A progressive decrease in these activities was however observed depending on the incubation time, regardless of the egg group (U or E). A discrete change in the profile of egg white proteins is also observed during incubation but no difference was noticeable between both groups (E versus U). To conclude, the antibacterial activity of egg white proteins progressively decreased during egg incubation. This observation could result from the alteration of specific antimicrobial proteins. Taken together, these data support that the egg white antibacterial defence is altered during egg incubation, suggesting that new compensatory protection systems might be set up during embryonic development to overcome this apparent weakening.