It could be said that no study of funeral costume itself in the Heian period has been made so far, while studies of funeral ceremonies during that time have been done to a certain extent. This paper is presented in order to reveal the real picture of funeral costume in the Heian period by focusing on the Sofuku (the most important mourning dress worn by the people for expressing their deep sorrow and condolence on a specific day chosen after the passing away of a person). In the early years of the Heian period, there was no specific funeral costume. Standard and consolidated funeral costume started to emerge show in the middle or later part of the Heian period. The Sofuku (even for the emperor and his male subjects) was standardized in the middle of the Heian period. All were made of Nibiiro (dark grey color) hemp cloth and were of Houeki design (the armpits are sewn up). Near the end of the Heian period, the color of the Sofuku was changed to black and the Houeki design was changed to Ketteki style (with unsewn open armpits), while the hemp cloth itself remained unchanged.