There are many functional characteristics of exopolysaccharides (EPS) produced by lactic acid bacteria in fermented dairy products. In this study, 2 EPS-producing strains of Lactobacillus delbrueckii ssp. bulgaricus and 2 Streptococcus thermophilus strains were isolated from commercial and rural yoghurts and they were inoculated into whey and their effects on EPS production and viscosity of whey were monitored. Two pH applications (adjusted pH and free pH) and 3 incubation temperature (42, 36 and 42/36(sic)C) were performed. pH of samples was significantly affected by starter culture strains, pH adjustment and incubation temperature (P < 0.01). Generally counts of L. delbrueckii ssp. bulgaricus were found higher than of S. thermophilus (P < 0.05). Viable cell counts were significantly higher, in pH-adjusted samples and 42 C samples, than their relevants (P < 0.01). Higher concentrations of EPS were observed in pH-adjusted media than that in pH-free media (P < 0.01). Also 2-step (42/36(sic)C) and lower (36(sic)C) incubation temperature caused an increase in EPS production. Viscosity of samples greatly influenced from their EPS contents. The highest EPS concentration (676 mg/L) and viscosity (6.37 mPa. s) was determined in the sample that inoculated with S. thermophilus ST3 strain, incubated at 42/36(sic)C with pH-adjustment.