In this research we investigated the performance of in-line Erbium Doped Fiber Amplifier (EDFA) in 40 Gbit/s 8 channels wavelength division multiplexing (WDM) transmission system with NRZ-OOK modulation format and 100 GHz channel spacing. Different EDFA configurations: co-propagation (980nm) and counter propagation (1480nm) were used in order to find an optimal settings with minimal noise factor indicators. Results show that in general the pumping wavelength of 980nm gives a stable noise factor values within 4 – 4.5 dB both for 10m and 30m long fibers. With the increase of pump power and fiber length, counter-propagation at pumping wavelength of 1480nm provides noticeably high noise up to 9–15 dB.