A better understanding of aggregate-associated N mineralizers and nitrifiers is important from both ecological and agronomic perspectives since plant available N and its environmental fate are ultimately determined by microbially mediated N transformations at the micro-scale level. Our working hypothesis is that the distribution and activity of N mineralizers and nitrifiers vary with aggregate sizes which was examined in long-term (22 years) no till (NT) versus conventional tillage (CT) systems. Potential N mineralization, nitrification and their ratios were determined for five aggregate sizes (2 – 4 mm, 1 – 2 mm, 0.5 – 1 mm, 0.25 – 0.5 mm, and < 0.25 mm). Total soil C and N, and microbial biomass C and N were also measured for the five aggregates sizes. Independent of aggregate size, soil and microbial measurements were generally greater in NT than CT. While soil and microbial measurements varied with aggregate size, the degree of variation was inconsistent. Our results suggest that soil C and N contents were the primary factors, but aggregate-associated soil environments played secondary role in regulating the distribution and activities of N mineralizers and nitrifiers.