Free Space Optics (FSO) communication technology has attracted large attention because of its high data rates and security. FSO links experience disturbances due to atmospheric turbulence and pointing errors. The performance of the FSO system can be improved by adding an extra transmit aperture at the transmitter along with Alamouti scheme. In this work, the FSO based 2x1 Alamouti scheme is analyzed with a novel statistical channel model called Double-Generalized Gamma (DGG), which accurately describes turbulence-induced fading over a wide range of turbulence conditions. The main objective of this paper is to derive the symbol error rate (SER) of FSO system for M-PSK with Alamouti scheme under the effect of different atmospheric turbulence with and without pointing errors using moment generating function (MGF). The SER performance of the proposed scheme is compared without Alamouti scheme. We also compare the results of DGG with Gamma Gamma (GG) fading channel. The performance of DGG is observed to be more nearer to the physical conditions. Substantial gain is achieved by using 2x1 Alamouti scheme. © 2017 IAMOT.