A mat for bedsore prevention, on which the pressure against portions such as sacrum liable to bedsore is kept below 30 mmHg/cm , a critical value that causes bedsore if it lasts long. The mat comprises a bag-shaped body (1) having rectangular parallelepiped recesses in a central portion and both side thereof, and bag-shaped auxiliary supports (2) adapted to be fitted in the recesses. The auxiliary supports (2) are made several centimeters thinner than the body (1) to provide a difference in level. The body (1) is inflated with air, and the auxiliary supports (2) are filled with water to 60 % of its capacity. With the arrangement of the mat, a major part of the weight of a human body is applied on the body (1) but not much on auxiliary supports (2). Accordingly, sacrum, greater trochanter and ilium, which are liable to bedsore and supported by the sub-supports (2) receive lower pressure than other places supported by the body.