Bed sheet fastening system (100; 101) to retain at least a portion of a cover sheet positioned on a mattress, with respect to the mattress, said system comprising: a substantially oblong pressing element, configured to be positioned above the sheet, said pressing element having a first and a second terminal end, and anchoring means (10,11;12), configured to anchor said pressing element with respect to the mattress, said anchoring means comprising a ribbon element (10,11) constrained or constrainable, at an end portion (20,21), to said first end of said pressing element, said ribbon element (10,11) having a connecting element at a further end portion (30,31) for anchoring said further end portion of said ribbon element (10,11) to said second end of said pressing element or to the mattress, in a condition of use of the system, the overall configuration of said bed sheet fastening system (100; 101) being such that, when the pressing element is positioned at a portion of the sheet to keep it in contact with the mattress, and the further end portion of the ribbon element is anchored to maintain the pressing element in the predefined position with respect to the mattress, at least one covered housing compartment between the mattress and the sheet is defined, said housing compartment being delimited by a fastened portion of the covering sheet and from a perimetral edge of the sheet, said bed sheet fastening system (100; 101) being characterized in that said pressing element comprises a main body made of rigid material, optionally of metallic material, said main body being able to ensure the necessary rigidity to said bed sheet fastening system (100; 101) to ensure, during use, its non-deformability, thus ensuring the fastening of at least a portion of a cover sheet with respect to the mattress, considerably reducing the possibility of moving it. a substantially oblong pressing element, configured to be positioned above the sheet, said pressing element having a first and a second terminal end, and anchoring means (10,11;12), configured to anchor said pressing element with respect to the mattress, said anchoring means comprising a ribbon element (10,11) constrained or constrainable, at an end portion (20,21), to said first end of said pressing element, said ribbon element (10,11) having a connecting element at a further end portion (30,31) for anchoring said further end portion of said ribbon element (10,11) to said second end of said pressing element or to the mattress, in a condition of use of the system, the overall configuration of said bed sheet fastening system (100; 101) being such that, when the pressing element is positioned at a portion of the sheet to keep it in contact with the mattress, and the further end portion of the ribbon element is anchored to maintain the pressing element in the predefined position with respect to the mattress, at least one covered housing compartment between the mattress and the sheet is defined, said housing compartment being delimited by a fastened portion of the covering sheet and from a perimetral edge of the sheet, said bed sheet fastening system (100; 101) being characterized in that said pressing element comprises a main body made of rigid material, optionally of metallic material, said main body being able to ensure the necessary rigidity to said bed sheet fastening system (100; 101) to ensure, during use, its non-deformability, thus ensuring the fastening of at least a portion of a cover sheet with respect to the mattress, considerably reducing the possibility of moving it.