In this paper, the conditions for dyeing cellulose in red with anthocyan were suggested. Cyanidin and pelargonidin were used as anthocyan. The number of hydroxyl group in the B ring in the chemical structure of anthocyanidin is two in the former and one in the latter. The results obtained were as follows : Cellulose treated with acidic materials such as tannic acid or thyntan were dyed in red with anthocyan solutions adjusted to pH 2, 3.4 and 4. Then, the important factor to consider when dyeing in red with anthocyan is to ensure that the acidic materials are free from constituents which form chelates with anthocyan, and that the anthocyan molecule does not have the structure to form chelates with metal ions in the mordants. Silk was directly dyed in red effectively in an acidic solution of anthocyan.