Abstract. This paper presents the analysis of the effect of BER and Q-factor on free space optical communication system using the diverse wavelength technique. The visibility is gradually decreased due to attenuation effects such as weather conditions as the bit error rate increases. Despite this disadvantage, FSO performance could be further improved by using a wide range of wavelengths of the laser beam. The results show good performance for 1550 nm wavelength, where the wavelength can accommodate visibility for 6 km at link range of 1 km, and Q-factor 25 at the system performance BER = 10 -124 could improve the system by 67% compared to 850 nm and 785 nm wavelength ,which could enhance the system by only 2%. This clearly show that the superior capabilities of 1550 nm wavelength in handling attenuation problems and capability to reduce the power loss compared to 850 nm and 785 nm wavelength.