This study investigates biological treatment of fruit juice industry effluents in sequencing batch reactor (SBR), activated sludge reactor (ASR) and anaerobic upflow sludge blanket reactor (UASB). At anaerobic biological treatability studies, seed sludge was acclimated to the medium and 95% of COD removal was obtained within a few weeks. At the end of anaerobic study, organic loading rate was increased to 5 kg COD/m(3)-day and the hydraulic retention time was decreased to 2.3 days. At the aerobic biological treatability studies, 90-95% soluble COD removal was achieved for both wastewaters (sour cherry and apple) in SBR and in ASR. In addition to aerobic biological treatability studies, microbiological investigation, and kinetic and stociometric coefficients were determined. At the end of microbiological examination, fungi overwhelmingly dominated the system.