Abstract: A floor mat and a small animal rearing cage capable of healthfully rearing a small animal and eliminating the need of adding a specific breeding floor mat even when the small animal is bred, wherein the floor mat is laid on the floor of a rearing box forming the small animal rearing cage. The floor mat formed in a sheet having heat retaining property and flexibility has such a size that can enclose at least the body part of the small animal and laid on the floor of the rearing box so that walls of such a size that can hide at least the half of the body of the small animal can be formed. By utilizing walls formed with the meandering and overlapped sheet-like floor mat, the small animal assures a sleeping floor, an excretion place, and birth and breeding place where light and wind can be avoided. The sheet-like floor mat desirably has both water absorbency and deodorization property to suppress the occurrence of odor.