Aimed to provid a new approach for the exploitation of natural product oroxylin A,this reasearch focused on obtaining oroxylin A from baicalin by biotransformation applying endophytic fungus-Penicillium sp.R3 from Scutellaria baicalensis Georgi,identifying its biotransformation pathway and optimizing the fermentation conditions.The culture and biotransformation reaction were carried out in potato dextrose broth(PDB).Cell growth was measured by dry weight and the maximum biomass of Penicillium sp.R3 was gained on the day 4,then it entered the stationary phase.The biotransformation pathway was analyzed by the method of adding different substrates and the products were measured and identified by HPLC.After fermentation baicalin was converted to oroxylin A accompanied with baicalein which was identified as intermediate metabolite.Single factor analysis and orthogonal test were applied to optimized fermentation conditions.The optimal fermentation conditions were as follows:the liquid medium volume was 10% of the bottle;the concentration of inoculated spores was 1×10⁶-2×10⁶/mL and the temperature and shaker speed were 30 ℃,150 rpm respectively.The substrate baicalin was added on the day 3 with proportion of 0.08%,then the biotransformation process sustained 6 days.Under these optimal conditions the molar conversion rate and concentration of oroxylin A reached 42.44% and 177 mg/L respectively.The growth regularity and the biotransformation pathway of Penicillium sp.R3 was clarified,the stable and optimal conditions were obtained with a satisfactory yeild.All these findings lay a foundation for the further development and utilization of oroxylin A.