Acrylonitrile-butadiene rubber (NBR) elastomers are widely used in seal and tire industries. Physiochemical, surface and tribological properties of NBR exposed to a lubricant in a sealed mechanical contact may gradually change, in particular, at elevated temperatures. In this study, industrial-grade NBR elastomers were aged in two model non-additivated base oils, namely non-polar hexadecane (HEX) and polar Diethylene Glycol Dibutyl Ether (DGDE) at both ambient (298 K) and elevated (398 K) temperatures from 1 to 168 hours. Mass changes of NBR before and after ageing indicated that NBR had distinct ageing dynamics in different model base oils and at different temperatures. For NBR aged in nonpolar HEX, the rate of weight loss of the rubber was larger at 398 K compared to that at 298 K. On the contrary, distinct weight-gaining (swelling) dynamics were observed for NBR aged in polar DGDE at 298 and 398 K. Based on Fourier Transform Infrared (FTIR), liquid and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and Energy Dispersive Spectroscopy (EDS) analysis it was found that aldehydes and sulfur- and zinc-containing compounds were leached out from NBR aged in both HEX and DGDE. The results of tribological studies showed that the non-aged NBR has a good wear-resistance. NBR samples had a very similar surface topography before and after tribo-tests. However, the worn surfaces of NBR samples were characterized by fine scoring (abrasion) marks after ageing in both model base oils. This has been attributed to changes in the steel-rubber contact environment during the sliding process and degradation of mechanical properties of NBR after ageing. For one NBR sample (after ageing in HEX at 398 K) very stable friction in the steel-rubber contact was observed.