Light conditions requird for the green pigmentation of cocoons of Antheraea yamamai, and the pigments (blue and yellow ones) determining the cocoon color were examined. For production of green cocoons high intensity (4, 000 lux) light was found to be necessary at the time of gut purge. The degree of green pigmentation was dependent on the intensity of irradiation. Blue light was as effective as white light, whereas red and gren lights were ineffective. Removal of ocelli had no adverse effect on cocoon pigmentation in either light condition. The absorption spectra and solubility properties of the blue pigment suggest that it is a biliverdin whereas the yellow pigments, which are water-soluble, remain unclear. The increase in light intensity caused an increase in abundance of the blue pigment in the cocoons, but no change in the mount of yellow pigment. Thus, light perceived via an extra-ocular photoreceptor causes the accumulation of a bile pigment in the silk glands and therefore causes the formation of green rather than yellow cocoons.