Free space optical (FSO) communication is one of the most recently developed modes of wireless communication. FSO is a technique used to convey data carried by a laser beam through the atmosphere. While FSO offers a broadband service, it requires a line of sight communication between the transmitter and receiver. The atmosphere has effects on the laser beam passing through it. For instance, the quality of data received is affected by the scattering and atmospheric turbulence. The atmospheric turbulence is caused by both temporary and special random fluctuations of the refractive index along the optical propagation path. Clear air turbulence impairs the performance of the FSO due to the fluctuation in the intensity of the laser beam. By referring to the two criteria, namely bit error rate (BER) and signal to noise ratio (SNR), this work includes analysis of the effect of atmospheric turbulence on FSO systems in Yemen by using an appropriate model.