By tilting the crystals formed in an amorphous Pd80Si20 alloy during crystallization in a transmission electron microscope, three phases have been determined. The metastable phase P1 has a primitive orthorhombic unit cell (a = 0.46, b = 1.37, c = 1.69nm) and its possible space group is Pnmm or P(nm21). Using the data of crystal P1 the EDP of MSII and Pd9Si2 phases reported by Masumoto et al and Duhaj at el respectively can be explained. The metastable phase F has a face-centred orthorhombic unit cell with the same values of a and b as the P1 phase but c = 1.46 nm. The phase P2 crystallized at high temperature has a primitive orthorhombic unit cell (a = 0.39, b = 0.76, c = 0.54nm).