Cinnamaldehyde was covalently bound to the ε-amino group of lysyl residues of lysozyme by reduction with sodium borohydride. This paper describes the enhanced antimicrobial activity against both the Gram negative Escherichia coli and the Gram positive Staphylococcus aureus compared with the activity of lysozyme, cinnamaldehyde or mixtures of both. The minimal inhibition concentration (MIC) of the new product against E. coli and S. aureus was determined for its possible use as a preservative in cosmetics as well as pharmaceuticals. Moreover, microbial efficacy was studied in cream/gel model preparations and a preservative effectiveness test with the complete microbial spectrum from demineralized water for three different dermatics (cream, gel) was used. Samples examined 1, 7 and 28 days after manufacturing demonstrated a ten-fold reduction in bacterial growth. The results suggest a possible utilization of lysozyme-cinnamaldehyde conjugates as preserving agents.