  We study the low-energy effective theory in N=2 SU(Nc) supersymmetric QCD
with Nf =< 2Nc fundamental hypermultiplets in the Coulomb branch by microscopic
and exact approaches. We calculate the one-instanton correction to the modulus
u=< 1/2 Tr A^2 > from microscopic instanton calculation. We also study the
one-instanton corrections from the exact solutions for Nc=3 with massless
hypermultiplets. They agree with each other except for Nf=2Nc-2 and 2Nc cases.
These differences come from possible ambiguities in the constructions of the
exact solutions or the definitions of the operators in the microscopic
theories.
