The application of leather dressing and lubricants is one of theimportant challenges in conservation of historic dry leathers,due to their effects on structural and visual properties andstability of leathers. This study aimed to investigate influenceand stability of silicone oil and polyethylene glycol (PEG) ontreated dry leathers, and application assessment of ascorbic acid(AA) as an antioxidant additive for PEG. The polymers,untreated and treated leather samples were submitted to heataccelerated ageing process. FTIR spectroscopy, colorimetry, pHmeasurements, investigation of mechanical properties andshrinkage temperature (Ts) were used to explain effect oftreatments. Also, the oxidation of polymers during ageingprocess was monitored by FTIR spectroscopy. Results showedthat silicone oil has better stability against thermal oxidationwith compared to PEG. Ascorbic acid inhibited the PEGoxidation. Moreover, results revealed that the silicone oil has abetter performance in treatment of dry leather than PEG orPEG+AA, due to its high stability and minimum changes invisual, structural and mechanical properties in treated leathers.