Abstract The spinodal decomposition process in Fe( 1− x )Cr x has been determined by measuring the critical scattering. The and 0.6. The spinodal and magnetic phase diagrams have been determined by measuring the critical scattering. The temporal variation of the scattering functions S ( k, t, T a ) has been studied at room temperature, after the sample had been annealed at T a for a time interval t , followed by quenching. A remarkable result is that S ( k, t, T a ) of Fe 0.6 Cr 0.4 and Fe 0.7 Cr 0.3 are almost identical for the same annealing temperature, in spite of the fact that Fe 0.7 Cr 0.3 was annealed above the spinodal line. This fact, together with the observation that S ( k, t, T a ) converges into the Lorentzian c /( κ 2 ( T )+ k 2 ) with very small very small κ(κ 2 ⩽0.01 A 2 , is explained well by the recent nonlinear theories of Langer or Saito.