Second phases in the melt-overflowed Al-Fe-V-Si alloy have been investigated, and found to be classified into three different types : e.g. icosahedral phase, hexagonal phase, and bcc α-AlFeSi. Crystallographic orientation relationships among the phases were determined by electron diffraction. All the phases have similar atomic arrangements, which are constructed by several (Fe+V) and (Al+Si) icosahedra connected through chains of (Al+Si) octahedra, and thereby providing close orientation relationships among them. Phase decomposition behavior of the second phases has been also investigated by means of hot-stage in-situ TEM technique. During heating icosahedral phase transforms to thermally more stable bcc phase, and such transformation is controlled by Si diffusion. On the other hand, transformation of the hexagonal phase to bcc phase is not controlled by diffusion.