Differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to determine morphological, structural and surface changes (biodegradation) on thermo-oxidized (80 degreesC, 15 days) low-density polyethylene (TO-LDPE) incubated with Aspergillus niger and Penicillium pinophilum fungi, with and without ethanol as cosubstrate for 31 months. TO-LDPE mineralization by fungi was also evaluated. Significantly morphological and structural final changes on biologically treated TO-LDPE samples were observed. Decreases to three units on crystallinity and crystalline lamellar thickness (0.4-1.8 Angstrom), and increases in small-crystals content (up to 3.2%) and mean crystallite size (8.4-14 Angstrom) were registered. An oxidation decrease (almost twice) on samples without ethanol with respect to the control was observed, while in those with ethanol it was increased (up to 2.5 times). Double bond index increased more than twice from 21 to 31 months. The higher TO-LDPE changes and fungi-LDPE interaction was observed in samples with ethanol, suggesting that ethanol favors the TO-LDPE biodegradation, at least in case of P. pinophilum, probably by means of a cometabolic process. Mineralization of 0.50% and 0.57% for A. niger, and of 0.64% and 0.37% for P. pinophilum were obtained, for samples with and without ethanol, respectively. A model to explain morphological and structural changes on biologically treated TO-LDPE is also proposed.