The Lyotropic Phase Behaviour of 1,2 Dialky 1 - 3 - B-D - Xylopyranosyl-SN Glycerol / Fatty acid Mixtures in excess Water have been studied using x-ray Diffraction . It has been observed that like the fully hydrated PC/FA and 1,2,-B-GalDAG/FA mixtures, the phase behaviour of fully hydrated 1,2-B-D-XyloDAG/FA 1:2 is also quite different both from the phase behavour of fully hydrated pure 1,2=B-XyloDAG, and of pure fatty acid. The fully hydrated 1,2B-XyoDAG with chainlengaths C - C exhibit lamellar (L[b]) and H phases, and those with chainlengths C - C Exhibit lamellar (L[b]), H and inverse micellar Fd3m phases. whereas the fully hydrated 1,2-B-DXyloDAG/FA 1:2 mixtures with C - C tend to form mainly lamelalr L[b] and inverse micellar Fd3m cubic phases. The mixture with a chainlength of C was found to adopt the lamellar ([b]) phase and a novel, presumbley inverse micellar cubic phase, which has not yet been indexed.