Free space optical (FSO) communication is a cost effective and high bandwidth access technique. A major impairment in FSO links is turbulence induced fading which severely degrade the link performance. Spatial diversity is one of the mitigation techniques for atmospheric turbulence to improve the bit error rate performance. In this paper, spatial diversity with equal gain combining (EGC), OOK modulation scheme with direct detection at the receiver are considered. An improvement in performance with spatial diversity is observed both at weak and strong turbulence level. At very strong turbulence level, a significant improvement in diversity gain is seen when the number of receivers are large though at the cost of increase in system complexity. © 2014 IEEE.