The aim of this study was to develop a new natural preservative system making up for the weak points of chitosan as a preservative. As reported in a previous manuscript (20th IFSCC Congress, Cannes, France, 1998), the minimum inhibitory concentrations (MICs) of water-soluble chitosan against bacteria and yeast were 0.9-3.0 mg mL(-1), whereas MICs of chitosan against Aspergillus niger were over 5.0 mg mL(-1). However, the result of recent study showed that the MICs of Inula helenium L. extract against A. niger were below 1.0 mg mL(-1). Thus, we could develop a new preservative system containing both chitosan and I. helenium L. extract named CI-mixture. MICs of CI-mixture against bacteria and fungi (yeast and mould) were 2.0-4.0 mg mL(-1). When 10.0% of the mixture (the ratio of chitosan to I. helenium L. extract = 7.5% : 2.5%) was applied to cosmetic formulae such as skin lotion, milk lotion, cream and pack, it revealed appropriate preservative efficacy. Our result of the patch test also showed that this preservative system reduced skin irritation by about 30-50%, as compared to the organic preservative system. Therefore, the good natural preservative system including chitosan and Inula helenium L. extract could be incorporated in cosmetic formulations.