By means of light scattering, the static critical behavior was investigated for symmetrical polymer blend solutions of polystyrene/poly(methyl methacrylate)/deuterated benzene and polystyrene/poly(2-chlorostyrene)/deuterated benzene with different polymeric indices N and polymer concentrations c. The temperature dependence of the isothermal susceptibility S-T and the correlation length xi(t) near the stability limit showed the static crossover from the mean-field to the three-dimensional Ising behavior in all solutions. The Ginzburg number Gi(BK) was evaluated with the aid of the crossover function of Belyakov and Kiselev. As c increases from the semidilute region to the bulk limit, the scaledGinzburg number gi(BK) = Gi(BK)N decreased, with the power alpha of gi(BK) proportional to c(alpha) being -1.25 to -2 as expected by the theory based on the blob concept. The values of gi(BK)(bare) evaluated by the bare interactions were smaller than experimental values.