Among all groups ofmicroorganisms, diazotrophes play important role inN mineralization in an ecosystem. Species Diversity is often used as a measurement of functional diversity at substrate level utilization by specific enzyme activities like Urease, L-Asparaginase, L-Glutaminase, Amidase, etc. Mathematical indices that describe the species richness, species evenness and Shannon-Weaver Index (S.W.I.) is used for measurement of diazotrophic diversity indices. In present study S.W.I. is measured for diazotrophes and correlated with functional diversity for substrate level utilization by specific enzyme activities viz.,Amidase and L-Glutaminase. Soil sampleswere collected at 0-10 and 20-30 cms depth fromfour different sites around Patan city during Monsoon and Post monsoon seasons duringMay 2001 to June 2002.