The synthesis and characterization of (alpha-DT-TTF)(2)[Au(mnt)(2)] is reported. The magnetic properties of this new salt show that it is still a rare example of an organic spin-ladder. (alpha-DT-TTF)(2)[Au(mnt)(2)] shares the same ladder structure of the DT-TTF and ETT-TTF analogues, and its room temperature conductivity is similar to 2 S/cm. Despite the observed donor orientation disorder associated with the thiophenic sulfur atoms, the intermolecular interactions between donor units, calculated using the extended Huckel approximation and a double-xi basis set, show that the interaction values do not depend on the configuration of the sulfur atom on the thiophenic ring. The insensitivity of the spin-ladder magnetic properties to the donor molecular disorder in (alpha-DT-TTF)(2)[Au(mnt)(2)] is a direct consequence of the negligible contribution of the disordered thiophenic sulfur atom to the HOMO. In the related donor ETT-TTF, this contribution is significant and destroys the magnetic interactions, and no spin-ladder is observed. This compound not only enlarges the number of organic spin-ladder systems in this series of closely related compounds but also provides an interesting example of weakly disordered molecular spin-ladder system.