Kojic acid is one of the active ingredients for facial lightening product. The need for kojic acid increases with increasing interest of many people with facial lightening product. However, kojic acid raw materials in Indonesia are still imported. So, there was an attempt to produce kojic acid independently. Kojic acid is a secondary metabolite produced by the mold of genus Aspergillus and Penicillium. This research aimed to analyze the effect of mixing phase and inoculum concentration of Aspergillus oryzae and Aspergillus tamarii cultures on kojic acid production. The levels of kojic acid were determined by UV-Vis Spectrophotometry method at 268 nm wavelength. The variation of mixing phase and inoculum concentration of mold cultures was carried out gradually. The mixing phases of cultures studied were at the beginning of preculture, the beginning of log phase and the end of log phase. Meanwhile, the variation of inoculum concentration were 1:1, 2:3 and 3:2 (Aspergillus oryzae : Aspergillus tamarii). The results showed that the highest concentration of kojic acid in stirred-bioreactor was obtained in fermentation cultures with the beginning of preculture using 1:1 ratio of inoculum, which produced 0.3436 g/L of kojic acid. This result has a great potential to be increased to a larger scale bioreactor.