1. Using genetically blocked yellow mutant of Aspergillus sojae 260, some environmental conditions which favor the Conidial color change from yellow to green were investigated.2. In the presence of culture filtrate or mycelial mat extract of other fungi, the yellow conidia of the Y1 strain changed their color into green. However, the degree of greenization with these substances was not so sufficient as to make it possible to draw a decisive conclusion.3. With the presence of copper and chlorine ions, the yellow color changed almost completely to green. The other halogens such as bromine and iodine could replace the chlorine ion. The color change was proved to occur only in yellow mutants of Asp. Sojae and Asp. oryzae. Other mutants such as white and brown ones did not show such a phenomenon.4. The green conidia thus obtained returned to yellow when they were transplanted on the ordinary media such as Czapek's agar and malt extract agar. It is apparent, therefore, that the color change was merely physiological modification.5. For the development of green color, the original green strain required copper ion, but the yellow mutant required both copper and halogen ions.6. The possible role of halogen ions and that of copper ions in inducing green conidia formation were discussed.