Many pine trees could secrete oleo-resin when they were wounded. The oleo-resin was a mixture of turpentine and rosin. After evaporation of volatile turpentine, rosin remained and covered the wound to protect wood from fungi and insects. From this point, rosin protects wood naturally. However, rosin is not bioactive against most wood decay fungi. In this report, a bioactive rosin derivated, quaternary ammonium salt (QAS), was synthesized and its bioactivity against some wood decay fungi was tested. Firstly, the rosin was esterified by epoxy chloropropane with the mole ratio of 1:2, the reaction time of 3.5h at 90°C. The intermediate was 3-rosin acyloxy-2- hydroxypropyl chlorine. Then, the intermediate reacted with demethylamine to produce N-(3-rosin acyloxy- 2-hydroxyl) propyl-N, N dimethylamine at the following conditions: their mole ratio of 1:2, reaction temperature of 80°C and reaction time of 2.5h. Finally, the N-(3-rosin acyloxy-2-hydroxyl) propyl-N, N dimethylamine was quaternized by epoxy chloropropane with the mole ratio of 1:1, the reaction time of 3h at 90°C, and the yield was 72.8%. The chemical structure of the product was identified by FTIR and 1H NMR. The QAS content of the product was characterized by gravimetric analysis with sodium tetraphenylborate as its precipitation reagent, and liquid chromatography analysis (LC) analysis. The antifungal activity of the product was determined by paper-disc method with wood decay fungi such as Trametes versicolor, Gloeophyllum trabeum and wood stain fungi such as Aspergillus niger and Paecilomyces variot Bainier. The anti-fungal experiment results signified that the QAS of rosin is active to these fungi, especially Gloeophyllum trabeum. Since it is produced easily from rosin, which is renewable and not expensive, QAS of rosin could be a potential wood preservative. Further study is planning.