Ammonia Selective Catalytic Reduction (SCR) is adapted for a variety of applications to control nitrogen oxides (NOx) in diesel engine exhaust. The most commonly used catalyst for SCR in established markets is Cu-Zeolite (CuZ) due to excellent NOx conversion and thermal durability. However, most applications in emerging markets and certain applications in established markets utilize vanadia SCR. The operating temperature is typically maintained below 550°C to avoid vanadium sublimation due to active regeneration of the diesel particulate filter (DPF), or some OEMs may eliminate the DPF because they can achieve particulate matter (PM) standard with engine tuning. Further improvement of vanadia SCR durability and NOx conversion at low exhaust gas temperatures will be required in consideration of future emission standards. A high-porosity substrate (HPS) with increased vanadia catalyst loading is a viable solution to reach higher conversion efficiency targets at low exhaust temperatures (<300°C).A previous study evaluated HPS of various design configurations with a high vanadia catalyst loading with a gas reactor and an on-highway 7L class engine . The study demonstrated HPS with high vanadia catalyst loading improves NOx conversion and has a potential to be downsized more than 50% when compared to standard substrate with conventional catalyst loading.This study addresses hydrothermally aged SCR performance of high vanadia catalyst loading on HPS in various design configurations. The catalyzed substrates were hydrothermally aged for 100 hours at 550°C with the engine and evaluated by measuring NH3 storage and performance over steady state conditions and the World Harmonized Transient Cycle (WHTC). For the transient test, 50% volume SCR was also tested to clarify effect of downsizing. The comparison of degreened and aged SCR performance confirms that HPS with high vanadia catalyst loading maintains high NOx conversion activity after 100 hours aging at 550°C even when the volume is cut in half. Also, the best SCR design in terms of tailpipe NOx and N2O emission is discussed in anticipation of tighter NOx and greenhouse gas emission (GHG) regulation.