Soil enzymes released by microorganisms play a significant role in N mineralization process that determines N availability for plant growth. Soil aggregates of different sizes provide diverse microhabitats for microorganisms and therefore influence soil enzyme activities. We hypothesize that enzyme activities involved in N mineralization are greater in macroaggregates than in microaggregates. Potential activities of N acetyl glucosaminidase, arylamidase, L-glutaminase and L-asparaginase were measured in five soil aggregate fractions(<0.25mm,0.25-0.5mm,0.5-1mm,1-2mm, and 2-4mm) obtained from soils of three different (No-till,chisel and moldboard) long-term (22 yr) tillage systems.  All of the four enzyme activities were significantly correlated with potential N mineralization. N acetyl- glucosaminidase, L-glutaminase and arylamidase activities of intermediate (0.5-1 mm) aggregate size were significantly greater (p <0.05) than macro and microaggregate fractions. However, L asparaginase activity did not vary significantly among aggregate sizes but did differ among tillage systems.  Both L-glutaminase and L-asparaginase activities are more strongly correlated with aggregate-associated total C(r=0.90; r=0.95 p<0.0001) and N(r=0.98; r=0.89 p<0.0001) than with microbial biomass C(r =0.85 p<0.0001; r=0.60 p<0.01).This shows that L-asparaginase activity is limited more by total carbon than by microbial biomass. N acetyl glucosaminidase and arylamidase activities were more highly correlated with aggregate-associated microbial biomass C(r=0.93 p<0.0001; r=0.64 p<0.01) than with total C(r=0.69 p<0.05; r=0.30 p=0.28). This implies that aggregate-associated microbial population enhances the activities of enzymes (N acetyl glucosaminidase and arylamidase) involved in polymer breakdown, the critical stage in N mineralization process. Further research may give a clear picture about whether specific groups of aggregate-associated microorganisms are involved in production of these enzymes.