Phase separation in the amorphous alloy annealed at 620 and 643 K has been investigated by means of the in situ small-angle neutron scattering (SANS) technique. The alloy decomposes into two supercooled liquid phases, with the volume fraction of about 10 - 20% for the second phase. The interphase boundary causes scattering behaviour. The phase separation rate depends strongly on temperature, with a rather sluggish coarsening in the late stage. The kinetic exponent of this coarsening stage was found to be about 0.06, to be compared with the Lifshitz - Wagner exponent, 0.33.