Electrospinning is an easy and economical production technique to produce nanofiber/nanofibrous webs from different polymers, polymer mixtures, inorganic materials, supramolecular structures and composite materials. These nanofibers have unique physical/chemical properties due to their large surface areas and highly nanoporous structures. Since these nanofibers have superior properties, various functions and can be modified by physical/chemical methods, they have a great potential to be applied in membrane/filter applications. Bioremediation is a commonly used technique for removal of water contaminants, and different kinds of bacteria have been used for bioremediation of water systems. Use of biointegrated hybrid materials is an alternative approach for bioremediation, and this may provide higher efficiency, ease of application and reusability. As a carrier system, electrospun nanofibers are suitable materials for integration of bacteria, since electrospinning can allow production of nano/micro scale composites with tunable physical/chemical properties. In this thesis, it was aimed to integrate bacteria that have bioremediation capability with electrospun nanofibers by using immobilization/encapsulation techniques and test the potential of these biocomposites for treatment of contaminated water systems. The integration of bacteria that can remediate ammonium, heavy metal, textile dye and surfactant with electrospun nanofibers was achieved by two different approaches. In the first approach, bacterial cells were physically immobilized on cellulose acetate (CA), polysulfone (PSU), polystyrene (PS), polycaprolactone (PCL) and polylactic acid (PLA) electrospun nanofibers. In order to observe effects of nanofiber/nanofibrous web morphology and arrangements on the immobilization of bacteria, some of these nanofibers were produced as porous, parallelly arranged, and with different diameters. In the second approach, by using polyvinyl alcohol (PVA) and polyethylene oxide (PEO) polymers, simultaneous encapsulation of bacteria in nanofiber structures was provided. Afterwards, all these different kinds of biocomposites were tested for their remediation potential in accordance with the intended use of the integrated bacteria.