Efficiency of a biological wastewater treatment process depends on microbial diversity and their ability to degrade specific pollutants. The aim of this study was isolation and identification of predominant microorganisms associated with pharmaceutical wastewater pre-treatment process and evaluation of a chemical oxygen demand (COD) removal efficiency of each individual isolate. There were 65 microorganisms isolated from activated sludge of the JSC “Grindeks” industrial wastewater biological pre-treatment process and subsequently tested for COD reduction in pharmaceutical wastewater containing 2300-3500 mg/l of COD. Out of all isolates 9 bacteria, 5 yeasts and 3 filamentous fungi showed COD reduction. The highest COD reduction levels among all isolates were observed from filamentous fungi Fusarium udum (88.7%) and Fusarium solani (89.4%). The most effective bacterial strains were Aeromonas caviae and Sphingobacterium thalpophilum, with 78.1% and 75.9% COD removal, respectively. Rhodotorula mucilaginosa was the most effective yeast strain and achieved 76.6% COD reduction.