Cloud- induced fading is occasional but one of the main impairments affecting free– space optics (FSO). In this paper, the bit error rate of intensity modulated FSO with direct detection (IM/DD) in single–input single–output (SISO) over Ray Leigh fading channels has been represented. It has been assumed that a single information-bearing signal is transmitted over fading channels. Only the effects of amplitude fluctuation have been considered. The expression for BER by finding the conditional probability of Bit Error has been expressed, for given amplitude fading and then averaging the conditional probability. The analytical derivations are built upon by considering that perfect inter symbol interference (ISI) due to broadening of the optical pulses arriving at the receiver. The performance of the FSO link by quantifying BER for different carrier wavelengths and for various transmission bit rate of the communication over cloud-induced fading channel has been investigated