An adjustable mattress structure comprises a mattress body in which there are a plurality of hollow bases, a plurality of elastic support units, a plurality of adjustable positioning boards and a plurality of spring positioning bodies. Each of the elastic support units consists of a first encapsulated elastomer and a second encapsulated elastomer. The first encapsulated elastomer depends on spring positioning bodies to be fixed on one of the hollow bases so that the second encapsulated elastomer extends inside the hollow base. Each of the adjustable positioning boards is fixed inside a hollow base and used to receive a second encapsulated elastomer; the adjustable positioning boards in the hollow bases are situated at distinct positions by which the adjustable positioning boards make the elastic support units generate distinct resilient bearing capacities for adjustable mattress firmness supporting a body curve.