In this research, we demonstrate 8 channels wavelength division multiplexing (WDM) transmission system with in-line Erbium Doped Fiber Amplifier (EDFA) using both co-propagation (980 nm) and counter propagation (1480 nm) EDFA configuration. The perfor- mance of an EDFA in a 40 Gbit/s 8 channel dense wavelength division multiplexing (DWDM) transmission system with NRZ-OOK modulation format and 100 GHz channel spacing was inves- tigated with an aim of finding optimal configuration. Results show that the pumping wavelength of 980 nm the usage of 15 m long doped fibers gain value is around 27 dB, thus the usage of 30 m long fiber already drives gain indicators close to 30 dB. With the increase of pump power and fiber length co-propagation EDFA configuration at pumping wavelength of 1480 nm provides noticeably high and stable gain values of more than 40 dB.