The purpose of the present invention is to provide composite particles for imaging that have high biodegradability after imaging. To achieve the above purpose, the composite particles for imaging according to the present invention are configured such that the ratio (long-term residual amount/short-term residual amount) of a long-term residual amount, which is the average value of the contrast rate after six days in a cell and the contrast rate after 11 days in a cell of the same type, and a short-term residual amount, which is the contrast rate after two days in a cell of the same type, is less than 99%.
