Abstract: A plant for pasteurizing or sterilising solid or liquid food products subjects the previously packaged products to heat treatment using microwaves in a pressurized chamber, in order to guarantee its conservation for long periods of time. At least three phases of operation include a rapid heating phase of the products, up to a temperature which is slightly lower than the pasteurizing or sterilising temperature; and a temperature equalising phase, and a cooling phase. The pressure inside the pressurised chamber, during the phases varies as a function of the temperature reached by the products. The plant includes a number of tubular elements (2, 3, 4; 11, 12, 13, 14), each of which consists of a number of sections (2a, 3a, 4a; 11a, 12a, 13a, 14a) cylindrical in shape and of a small diameter, each tubular element having devices for inserting and removing from it the products to be treated and for varying the ambient pressure inside it, as function of the temperature reached by the products.